1038

R E P O R T ON T H E A C T I O N OF S U N L I G H T ON

A E R O P L A N E F A B R I C ; ITS N A T U R E AND P R E V E N T I O N .

By F. W. ASTON, D.Sc.

Presented by the SUPERINTENDENT, Royal Aircraft Fac tory .

Reports and Memoranda, No. 396. Oclober, 1917.

SUMMARY.--OI all the agents tending to the deterioratiofl of aeroplane fabric when exposed to weath(r, sunlight is the most important. The part of sunlight effecting this deterioration is shown to lie between X = 4000 and X - 2950, and is therefore invisible. The action is probably an oxidation, and a possible explanation is formulated, based on theoretical photo-electric considerations. The behaviour of the quartz merc~ly lamp used in the investigation is discussed. Means of prexentirg the action of light are considered, and it is shown that although the vast majority of dyes are unsuitable, at least one black dye, if used in proper quantity in the dope, renders the latter practically light proof.

INTRODUCTION.

Experiments extending over three years and involving many thousands of strength tests confirm the conclusion that deteriora- tion in strength of doped or undoped linen fabric (sometimes known as " Tendering ") when exposed to ordinary service conditions is due to light and to light only, the effect of other agents, e.g., heat, moisture, bacteria, moulds, &e., being quite inappreciable in comparison. The following is an account of experiments made with a view to obtaining some information on the nature of the act ion of light, with the object of its prevention.

As a physical s tudy the problem is beset with difficulties. The material upon which the work has to be done, whether ya rn or fabric, being a manufac tured article, is exceedingly variable in its properties, a defect great ly enhanced by the exigencies of the war, so tha t it is necessary to use statistical results involving either large numbers of experiments or low numerical accuracy.

Again, it is difficult to imagine a more unreliable quan t i ty than sunlight in this country, so tha t there can be no comparison between the two tests unless they have been exposed for an identical period both in dura t ion and date. The only artificial source of light ye t used with any success is t ha t of the quar tz

1039

mercury are, and this is found to be subject to serious objections. I t is not therefore surprising that discordant or even contra- dictory results are occasionally obtained, and the greatest care has t~ be used ~o avoid erroneous conclusions.

THE I)ISTRIBUTIO~I OF DESTI~UCTIVE PO~VER IN THE ~PECTRUM°

This was investigated by the direct method of throwing the spectrum of mercury arc on a series of linen threads, using for the purpose a Hilger Quartz Spectrograph, kindly lent from the Cavendish Laboratory by Prof. Sir J. J. Thomson.

The method adopted was as follows : -

Two photographs of the spectrum to which the linen thread was to be exposed were taken on a ~ plate in the ordinary way, one at the top and one at the bottom of the plate. After the finished negative had had its edge carefully rounded off the whole of the spectrum was covered by a binding of thread, the strands of which were carefully laid close together parallel to the spectrum lines. The thread used was Campbell's No. 70 special machine linen thread which had been washed free from size. As wound on the plate, there were almost exactly three threads per mm., rather over 100 being used to cover the part of the spectrum judged to be important.

The negative was now replaced in the plate holder of the spectrograph and exposed exactly as an ordinary plate, using the threads as a sensitive surface, the plate holder being in its median position.

When the experiment was originally planned, it was hoped that the loss of strength of each thread could be plotted along the spectrum, but this was not practicable owing to the im-. possibility of obtaining threads of sufficiently uniform strength, and also to the unexpectedly feeble destructive power of the dispersed light. Fortunately, however, there was available a much more delicate criterion, capable of giving useful results, namely, observations showing which threads broke at the point of application of the light and which broke elsewhere.

Even with the employment of this method, the first two experiments g~ve completely negative results, although the exposure in the second case was prolonged for 250 hours. ]n searching for the causes of the failure, an explanation was soon found in the rapid falling off of ultra-violet efficiency of the mercury arc, dealt with in detail below. A third at tempt was therefore made, the conditions of which, as it was successfld, will be now described.

The source of light was a Westinghouse Cooper-Hewitt Quartz Mercury Arc, type Z.2B., taking about 3.5 amperes at 200 volts. In .order to obtain maximum intensity, the burner was arranged parallel to the slit of the spectrograph upon which

1040

the image of the arc was projected by means of a short focus quartz lens in line with the collimator. A very open slit was used, giving lines about 2 ram. wide at the plate (v. spectrum No. 1), i.e., covering about 6 threads. The total distance travelled by the light in air was about 75 cms.

The duration of the exposure was four weeks, the lamp being interrupted to change the burner, which was done five times in all. Plates bound with threads were exposed to the direct fight rays for varying periods as checks, and tested from time to time in order to form some idea of how the lamp was lasting, and other experiments not connected with this particular research, but requiring the use of the lamp, were carried on at the same time. At the end of the exposure the threads were stuck down to the plate with a little varnish at the point immediately opposite t|la~ exposed, and then cut and tested one by one in order in a Baer Thread Tester. The breaking strain was recorded, but is of little interest in this particular experiment, as the real criterion taken was whether or not the thread broke on the part exposed to the spectrum. The position of the threads relative to the lines of the spectrum was checked from time to time as the breaking tests proceeded, and the diagram showing the results is given in Fig. 1. The line of circles represents the threads, those breaking on" the spectrum being shown black. As the latter occupied about a sixth of the length between the jaws of the thread tester, an average of one black circle in six is to be expected in the unaffected regions.

Above the threads are shown the lines of the mercury arc spectrum as a series of columns approximately six threads wide ; the heights of the columns represent the relative intensities. In the case of the stronger lines where wave lengths are given, the intensities are those determined by Ladenburg, the others being estimated roughly from the strength of the image in the photographic negative. For reference a curve showing the distribution of intensity in sunlight is included. This is plotted from Abbot and Fowles values corrected for the dispersion of the instrument.

The experiment shows very definitely tha t the destructive effect of the light from the mercury arc of greater wave length than ~ = 3660 A U. is negligible. As there is a strong line at

-= 4060, it is perfectly safe to conclude that in sunlight or in a continuous spectrum the destructive effect cannot be serious for ), > 4000; in other words, visible fight has little, if any, destructive effect. In the direction of smaller wave lengths there appears to be no limit, and it is doubtless due to this tha t there is so great a disparity between the effects of the direct light of the lamp and that in the spectrograph. Thus, at a distance of 45 cms., the direct fight caused a loss of about 20 per cent. per week, while the mean loss of strength over the whole dispersed spectrum for four weeks was inappreciable.

1041

Solne early experiments with the mercury lamp showed that its effect on the fabric was enormously reduced by the interposi- tion of a piece of window glass. Later it was found that glass did not reduce the effect of sunlight in anything like the same proportion. The explanation of this is quite clear when we compare the result of the thread test with the spectrum of the mercury arc through glass (No. 2 in the ph(itograph). The glass cuts off all rays less than X 3390, thereby reducing the destruc- tive energy of the mercury spectrum to a much greater degree than that of sunlight, which has but little energy below tha t wave-length.

TIIE INFLUENCE OF THE ATMOSPHERE SURROUNDING

THE FIBRES.

As ozone and H20 ~ have long been suspected of being the principal agents in the deterioration process, experiments in which oxygen and water are partially or wholly eliminated should give valuable results.

The first experiment of this ]Kind has already been described. I t consisted of exposing strips of aeroplane fabrics to the light of the mercury arc in a box with a quartz lid, and comparing its loss of strength when air or hydrogen was passed through ~he box. I t was found that a loss of strength of 20 per cent. in the case of air was reduced to 6 per cent. in the case of hydrogen. The method of experiment has been greatly improved by the use of linen threads instead of fabric strips, so that more test pieces can be taken and several different experiments can be exposed to the lamp at the same time, and so can be regarded as strictly comparable.

The procedure consists in winding the thread on glass, as in the spectrum experiment. A narrow strip of glass is taken, carrying about 30 test threads, and thick tinfoil is wrapped over the ends so tha t only the half inch at the centre of each test thread is exposed to the light. Test strips of this ldnd can be slipped into 15 m.m. transparent quartz tubes, in which they can be subjected to any treatment desired very much more conveniently than in the large box with quartz lid previously employed.

The following is a typical set of results. In this case four sets of threads were used, all being placed in similar quartz tubes. One of these tubes was open at both ends, so tha t air was free to circulate. The second contained phosphorus pentoxide at one end; it was highly exhausted for a considerable time in order to render the threads as dry as possible and then filled with dry air. The third was exhausted to a very high degree of vacuum on a Gaede Mercury Pump with repeated warming, and then sealed off. In a fourth was put a control strip of threads completely covered with tinfoil. The four tubes were placed

1042

under the mercu ry arc a t a dis tance of abou t 23 cms. A the rmo- me te r was laid be tween them which rapidly rose to 59°C. (a t e m p e r a t u r e which does not usual ly affect the s t rength of linen yarn) and then remained s t eady t h roughou t the exposure. After an exposure of 72 hours the th reads were tes ted and the posi t ion of b reak noted, the s ta t is t ical percen tage of breaks be tween the marks in unexposed th reads being a b o u t 16.6 per cent.

THREAD CAMPBELL'S NO. 70, NOT WASttED.

~Y[ean % Loss of Percentage of Threads Strength. S t r eng th . breaking on part exposed.

Air (not dried) ... Air (dry) . . . . . . Vacuum ... • .. Chcck in darkness ...

52"2 oz. 52'3 , ,

71 '5 ,, 79'5 ,,

34"4% / 34'2% 10.2O,o

10o% ]00% 62 % 16.6%

The conclusion f rom these and other similar exper iments is t h a t the r emova l of oxygen f rom the a tmosphe re surrounding the fibres ve ry largely reduces, bu t does not ent i re ly eliminate, the des t ruc t ive agtion of the light. The presence or absence of mois ture does not seem to be impor t an t .

TI~E BEHAVIOUR OF THE QUARTZ MERCURY LAMP.

[t was hoped t h a t the quar tz m e rcu ry l amp of s t anda rd p a t t e r n run a t cons tan t cur rent and vol tage could be regarded as a cons t an t source of u l t ra-v io le t light, bu t un fo r tuna te ly this hope is not fulfilled in pract ice, except for ve ry shor t periods. As the l amp is used, the walls of the quar tz burne r become more and more opaque to l ight of short wave length, unt i l a f te r a period va ry ing with individual burners f rom 50 to 200 hours running, the quar tz walls tu rn brownish yellow and the l amp becomes prac t ica l ly useless as a source of u l t ra-v io le t light, t hough its visible candle power is ha rd ly impaired. This effec~ is clearly shown in the accompany ing pho tog raphs of spectra .

No. 3 is the spec t rum of a me rcu ry arc t a k e n th rough the e m p t y glower of a new lamp. No. 4 the same, t a k e n th rough a similar e m p t y glower of a l amp which had been run abou t 200 hours ; bo th were given the same exposure. I t will be seen t h a t the in tens i ty of all lines shor ter t h a n X = 3660 is enormous ly reduced. The old burne r can be r e juvena ted b y admi t t ing air and heat ing in the oxy-hydrogen flame unt i l the quar tz softens, when the brown l a y e r - - w h i c h is p r e s u m a b l y due to s i l i c o n - :burns off completely . This r e juvena t ion can only be done a few times, as gas is l iberated in the quar tz and makes its appear - ance as minu te bubbles when this is melted, in the same m a n n e r as it does in the glass walls of old X r a y bulbs. After three or four re juvenat ions these bubbles render the burne r too opaque to be: useful.

1043

~=~HOTO-:ELECTRIC THEORY FOR TtIE ACTION OF LIGt tT .

I t will be seen that there is evidence that ozone, or oxygen in some active state, is the most important factor in the destruc- tion of linen fibres by light. Lyman (Spectroscopy of the Extreme Ultra-Violet, p. 67) has shown that light c£using the direct forma- tion of ozone in air must have a wave length less than 1850 A.U. and that it is completely absorbed by 1 mm. of air at atmospheric pressure. I t is therefore quite impossible that any appreciable quanti ty of ozone can be formed by the direct" action of sunligh~ on the air near the earth's surface. How then can we account for the production of ozone on or in linen fibres ? A possible explanation has been suggested by Dr. F. A. Lindemann, which may be briefly explained as follows : -

The most effective frequency , for ionizing a gas is given by h , = e V, h being Planek's constant, e the electronic charge and V the ionization potential. If we take V----9.0 volts, the value obtained by Frank and Hertz, we get ~ = 1380, a value agreeing very well with X = 1350 according to Hughes (v. Allen Photo-electricity, p. 90), but the energy required to

8 2 remove a charge e to infinity is of the form ]cr where ]; is the

dielectric constant of the medium* and r the radius of the mole- cule, so that the most effective wave length in a medium of dielectric constant t: will be k times that in oxygen itself, of which t h e dielectric constant is nearly 1. -Hence if we can determine lc for linen fibres, the most destructive region of the spectrum can be roughly predicted.

A direct determination of k is impossible ; but since it equals the square of the refractive index, it can be calculated if the latter is known. By the method of immersing the fibres in liquids of various refractive indices a value for linen fibres of 1-53 has been obtained. From this was obtained a value lc- -2 .34. which gives a wave length X ---- 3230 in good agreement with the actual results given above.

I t will be seen that this special reasoning only applies to molecules of oxygen which are actually in close contact with or adsorbed by the fibres. Such molecules would be exceedingly difficult to remove ent irely by pumping or washing with another gas, so tha~ a possible explanation is supplied for the incomplete immunity found in a vacuum or an atmosphere of hydroge n.

The above photo-electric theory suggests several experiments which will be performed as opportunity occurs.

. . 7 ~ - m ~ - - . . . . . . . . . . . . . . . . . . . . . . . . . . . : . . . . . . . . . . . : . . . . . . . . . . 7 7 - - : . . . . . . . . . . . : . . . .

* As t h e d i s t ances w i t h w h i c h we are conce rned here are c o m p a r a b l e w i t h molecu la r in te r spaces , k will nc~ h a v e i t s o r d i n a r y s ta t i s t i ca l m e a n i n g , b u t i ts numer i ca l va lue wil l p r o b a b l y n o t be v e r y different .

1044

METHODS OF PROTECTION OF FABRIC FROM SUNLIGHT.

There appears to be three possible ways of preventing the destructive action of light : - -

(1) Complete removal of oxygen from contact with the fibres.

(2) Treatment of the fibres with some material which would decompose the ozone as quickly as it is formed.

(3) Covering the fabric with a coat of some substance opaque to the destructive rays.

The first is not a practical method. The second is worth consideration ; but as the ozone is probably formed in the sub- stance of the fibre; it is not a hopeful one. The third method was adopted as soon as the importance of the effect of light was realised and resulted in the preparation of the now well- known P.C. 10, which is a pigmented varnish applied after the dope on all surfaces exposed to direct sunlight. If a sufficiently thick and even layer of this is applied, its protective power is practically perfect, as it cuts off all light.

Good as this protective varnish is, it is clearly advantageous to have a dope which is itself opaque to the destructive rays, for the following reasons : --

(1) As the dope is applied in several coats, it is easy to ensure tha t the protective layer is both uniform and sufficient.

(2) A finishing coat of any colour or material may be safely employed, and camouflage or protective disguise can be suited to any particular background or purpose (this seems likely to become increasingly important as aerial fighting is developed).

(3) The weight of the pigment may be saved.

Clearly the ideal substance is a colourless compound which may be more or less correctly termed a " dye " soluble in the dope, having an absorption band covering the whole of the ultra-violet from approximately )~ 2950 to k 4000, but not seriously destroyed by exposure.

Such a substance would be of fundamental assistance in the construction of a transparent aeroplane. That this is a theoretical possibility is indicated by the behaviour of such bodies as re- sorcinol, salts of quinine, &c., which have absorption bands in other parts of the ultra-violet. Pending its discovery, efforts have been made to find a coloured dye satisfying the conditions required.

So far 102 spirit soluble dyes have been tested, a list of which is appended, and 15 were not sufficiently soluble to be of a n y use. The remainder were tested for stability by exposure to

i)

i)

1045

sunlight and the mercury lamp. The most stable ones were now subjected to further examination by photographing the spectrum of the mercury lamp through a 1 per cent. solution of them in alcohol, contained in & small cell 1.3 mm. thick with quartz walls. In this way a good idea could be obtained of the absorptive power of the dye in the region required.

Several of these spectra are shown in the appended photo- graph together with that of the lamp when no dye was in the cell ior comparison. I t will be seen that all, with one exception, cut off the dangerous rays fairly well. The case of Rosaniline .Hydrochloride :No. 6 is an excellent illustration of the value o'~ the spectrograph in work of this sort, as it is an exceedingly stable dye and had all the appearance of being a most hopeful sample ; the spectrum, however, shows it to be useless on account of its transparency in the region k ~ 3660.

Six of the most hopeful and representative dyes were now chosen and 2 per cent. solutions used, instead of plain alcohol, in preparing dyed raftites, i.e., 0.5 per cent. solution of dye in the dope. The dyes were aurine, chrysoidine, maroon, crystal violet, gentian blue and spirit black. Frames doped with these dyed raftites were exposed, together with control frames, for 80 days of unusually bright summer weather from the beginning of June hntil late in August, 1917. If we leave the spirit black for later consideration, the behaviour of the first five dyed dopes can be easily summarjsed. All faded and all cracked earlier and to a greater degree than the undyed raftite. On the other hand, although in strength tests after exposure the dyed dopes were

s t ronger than the undyed one, the increase was not sufficient to warrant the use of any of these dyes.

With the spirit black, however, the results were entirely different and unexpectedly successful; there was no sign of cracking or fading, and on the strength test the fabric doped with the black dope gave the same figures as a comparison frame doped with ordinary raftite and two coats of P~.C. 10, showing that a perfectly practicable protection had beei~ attained with the dye alone.

I t is somewhat unlortunate that the most efficient dye is black, as, for ordinary day flying in these climates, khaki would be preferable. On the other hand, it is ideal for night flying, and has already been adopted for night-flying machines built at the R.A.F. For the tropics, also, it can be used with the thinnest possible coat of aluminium varnish to keep down the effect of radiant heat, obviating the necessity of the intermediate coat of P.C.10 or P.C.12.

As the quanti ty of dye used is 5 lbs. per 100 gallons of dope, the increase in weight is quite negligible.

1046

L I S T OF D Y E S .

Solubility in Alcohol.---N. = N o t S o l ' u b l e e n o u g h f o r u s e .

S S . = S l i g h t l y S o l u b l e . F S . = F a i r l y S o l u b l e . S. = S o l u b l e .

Stability to Light.--4 = V e r y S t a b l e . 3, 2, 1, 0 i n d e s c e n d i n g

o r d e r o f s t a b i l i t y .

No.

1 2 3 4 5 6 7 8 9

10 11 12 13 14 15 16 17 18 19 2o 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

Dye.

5 I a n c h e s t e r Ye l low . . . . . . . . . B r i l l i an t Ye l low . . . . . . . . . N a p h t h o l Ye l low . . . . . . . . Sp i r i t A u r i ne (Simpson') . . . . . . At , f ine (Greefl) . . . . . . . . . . . . Oral)ge N. (Badische) ... . . . . . . T r o p a e o l i n . . . . . . . . . . . . Au r i ne (Griffin) . . . . . . . . . Ch ryso id ine . . . . . . . . . . . . V e s u v i a n B r o w n . . . . . . . . . B r o w n A n t i q u e . . . . . . . . . Acid B r o w n (G. e x t r a ) . . . . . . Eo s i ne (GreefI) . . . . . . . . . . . . Ceres B r o w n ... B r o w n B lack lev V a n d y k e B r o w n . . . . . . . . . F u e r s t B r o w n . . . . . . . . . . . . Mode B r o w n . . . . . . . . . . . . B i s m a r c k B r o w n . . . . . . . . . P h e n y l B r o w n . . . . . . . . . . . . V e s u v i n . . . . . . . . . . . . . . . . S o u d a n . . . . . . . . . . . . . . . l ~ h o d a m i n e . . . . . . . . . . . . t¢osolic Acid . . . . . . . . . ... I ) i a m i n e F a s t R e d . . . . . . . . . R o s a n i l i n e H y d r o c h i o r i d e . . . . . . Hes s i an Pu rp l e . . . . . . . . . Sp i r i t ]~ose . . . . . . . . . . . . Spi r i t Rose (Fuer s t ) . . . . . . . . . E o s i n (Blue Shade) . . . . . . . . . E o s i n (Yel low shade) . . . . . . . . . b l a r o o n . . . . . . . . . . . . ... B r i g h t R e d (Fue r s t ) . . . . . . . . . C. R e d (Fue r s t ) . . . . . . . . . P o n c e a n ... . . . . . . . . . B e n z o p u r p u r i n e . . . . . . . . . D i a m o n d Green . . . . . . . . . R u s s i a n Olive . . . . . . . . . . . . S a p Green . . . . . . . . . . . . V ic to r i a Green . . . . . . . . . I o d i ne Green . . . . . . . . . . . . G u i nea Green . . . . . . . . . . . . Ma lach i t e G r e e n . . . . . . . . . Ceres Green . . . . . . . . . . . . Acid Green . . . . . . G reen No. 27045'(Fuerst)-- " - - . . . . . . Ani l ine Green . . . . . . . . . . . .

Solubility.

SS. SS. SS. S. S. FS. FS. S. S. FS. FS. FS. S. YS. FS. FS. FS. FS, FS. FS. I ;S FS. S. FS, YS, S. FS. S. S. FS. FS. S. S. FS. SS. SS. S. FS. FS. ~FS. FS. FS. FS. FS. FS. FS. S.

Stability.

0 0 0 4 4 1 1 3 3 0 1 0 0 0 0 0 1 1 0 0 0 0 0 0 0 4 0 0 2 0 0 2 0 0 0 0 1 0 1 1 1 0 1 1 0 1 1

% \

\

\

f

mi "Ui o l ~J

©

I!

o

R E P O R T 1~O. 3 9 6 . FIG. 2.

D E S C R I P T I O N OF SPECTRA IN P H O T O G R A P H .

No. 1. Spectrum of lamp as used in thread experiment, exposure 1/100 sec.

No. 2. Spectrum of Mercury Arc taken through window glass. No. 3. Same through burner of new lamp. No. 4. Same through burner of lamp used 200 hours. No. 5. Same through cell containing 1 per cent. solution of Aurine. No. 6. Same through 1 per cent. solution of Rosaniline Hydrochloride. No. 7. Same through 1 per cent. solution of Maroon. No. 8. Same through 1 per cent. solution of Gentian Blue. No. 9. Same through 1 per cent. solution of Spirit Black. No. 10. Same through 1 per cent. solution of Chrysoidine. A spectrum of the lamp taken through the cell when no dye was present

and a wave length scale are given below for comparison.

i I I I I I I I I I P .....

2 II ~ Illi l l l

3 11 II!.ti~llt~ll!ll~ll ~,

4 ,1 I I I , i

511!"

6 ~III

7 i~:.i

s I ~

I0 i i

I~IIII~II,' llr '

o o o o

o

1047

L : s T o ~ ~ D¥ns.--continued.

58 59 60 61 62 63 64 65 66 67 6g 69 70 71 72 73 74 75 76 77 78 7 9 80 8 l 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99

1 1 0 0

]01 102

No. Dye.

48 I3ri l l iant Green . . . . . . . . . 49 Vic to r i a B l u e . . . . . . . . .

50 B r i g h t B lue . . . . . . . . . 51 I n d u l i n e . . . . . . . . . 52 G e n t i a n Blue . . . . . . . . . 53 Sp i r i t B lue . . . . . . . . . 54 M e t h y l B lue . . . . . . . . . 55 M e t h y l Viole t . . . . . . . . . 56 M e t h y l e n e Blue . . . . . . 57 H e l i o t r o p e . . . . . . . . .

Sa f f r an ine . . . . . . . . . C r y s t a l Viole t . . . . . . . . . B l a c k No. 80544 (B r i t i sh Dyes ) B lack No. 80545 (Br i t i sh 1)yes) Sp i r i t B lack No. 18 (Lane Hall) Sp i r i t B l a c k No. 19 (Lane Hal l ) Sp i r i t B l a c k No. 20 (Lane Hall) Spi r i t B l ack (Ball) . . . . . . Sp i r i t B l ack ( J o h n s o n ) ... Sp i r i t J e t B l a c k (S impson) ... Sp i r i t B l a c k (S impson) ... Sp i r i t B l a c k (Bur ton ) . . . Nigros ine . Spi r i t Sol . . . . P r i m u l i n e ... . . . . . . Ch ryso l in Ye l low ... ... D i a m i n e F a s t Ye l low ... C h r y s o p h e n i n . . . . . . . . . T o l u e n e B r o w n . . . . . . D a r k B r o w n . . . . . . . . . I n d i g o C a r m i n e . . . . . . Congo IZed . . . . . . . . . C o l u m b i a Blue . . . . . . B. N a p h t h o l G r e e n . . . . . . N i g r o s i n e . . . . . . . . . B i e b r i c h Scar le t . . . . . . C o l u m b i a G r e e n . . . . . . N i g h t B lue . . . . . . . . . Azo Blue Yellow, No. 7921'0 (British Dyes ) Green , No. 7956,1 (Br i t i sh Dyes) Yel low, No. 80068 (Br i t i sh Dyes) I~ed, No. 80155 ( B r i t i s h Dyes) I~ed, No. 80262 (Br i t i sh Dyes ) Green , No. 81152 (Br i t i sh Dyes) B r o w n , No. 81153 (Br i t i sh Dyes) Green , ( J o h n s o n ) . . . . . . Ye l low ( J o h n s o n ) . . . . . . B r o w n ( J o h n s o n ) . . . . . . R e d ( J o h n s o n ) . . _ Yel low, No. 14499 ( S i m p s o n ) " Orange , tZ.S. (S impson) B r o w n , No. 14219 (S impson) ill tZed, NO. 14746 (S impson) ... Green , No. 14781 (S impson) .. . Black, No. 11631 (S impson)

I i Solubility.

. , , S .

... ! S.

. . . S .

. . . . i F S .

. . , S ,

° . . S .

... ~ SS.

"'" 1 F S . , . . S .

, , . S .

. , . S °

... I;S.

... I:S.

... FS. • '" i 1;S, ... FS. . . . I F S . ... ) FS. ... FS. ... ! [ :S . ... t;S. ... KS.

! N. i N .

• ' - I

N. "" i N. . , .

• .. i N . . " i 2N. ... ! N .

N. " " i N. • -. I N .

! N .

::: i x. • " I N . ° . . N .

... i N. SS.

: : : ! s s • "- I S . ... SS. • ,. i SS,

F S . : : : I s . . . i : s .

• . . i FS. ... ! ~SS. . . . I s s .

"'" / S . S.

"'" I FS. ... S S . "'" / SS. . . . . FS.

S L a b i l i t y .

1 0 o 4 4 4 l 1 o 0

1 1 2 3 4 4 2 4 4 3 3 4 4

2 4 1 1 2 1 3 3 1 3 4

1 2 3 4