152 ANALYTICAL EDITION VOl. 1, No. 3

experience is necessary before the appearance of a sample can be estimated exactly from the shape of the spectrophotometric curve. This difficulty will soon be solved by an attachment to the color analyzer which will compute mechanically the three primary sensations produced by a given sample. As the usual method of performing this computation is extremely tedious ahd unsuitable as a routine procedure, the writers have devised a much simpler one to fit the present case in an attempt to correlate their results with the other known properties of the many grades of flour. Since the maximum sensitivity of the normal human eye occurs a t 556 mp in the green, this point in the spectrum was selected as the basis for estimating the position of a specimen on a scale of grays. Thus the reflecting power of Sample 3 in Figure 2 at 556 mp is 88 per cent. Consequently, by definition, the brilliance score of this sample is 88. The yellowness of a sample de- pends principally on the degree of excitation of the primary blue sensation which has a maximum at 440 mp, If the height of the curve representing Sample 3 were 88 per cent a t this point, it would probably appear to be a neutral gray in color. The actual height is 79.7 per cent and the difference between this value and 88 per cent is arbitrarily taken as the yellow score.

This method of deducing the value of the color sensation from the spectrophotometric curve is only approximate, but it is satisfactory whenever all the curves have the same general shape, as was found to be true in this case. For example, Figure 2 shows a curve for a representative sample of a patent, straight, and bakers’ grade of wheat flour. The curves for all thirty-five samples were found to be of this general form and corresponded closely to the designated grade for samples ob- tained from mills which maintain color standards carefully. Although these results are of a preliminary character, the writers have attempted to correlate the computed color values with the other known properties of the samples. The results for thirty samples obtained from nine mills are given in the accompanying table.

MILL

VI11 VI IX VI1 I1 VI11 IX VI1 VI I 111 I VI1 I1 I11 , 111 IV IV V I1 V I 111 111 VI V I1 IX IX 111

ASH^ Per cent 0.334 0.345 0.404 0.380 0 .394 0 .441 0.404 0 .400 0.442 0.392 0 ,460 0.447 0.620 0.386 0.395 0.395 0.450 0.410 0.393 0 .433 0 .418 0.668 0.659 0.460 0.536 0.588 0.534 0.659 0.659 0.650

Experimental Da

GRADE

Patent Patent Patent Patent Patentb Straight Straight b Straight Straight Patent Straight b Straight Bakers’ Patent Patentb Patent Straight Patent Patent Straight Straight Bakers’ Bakers’b Straight Bakers’ Bakers’ Bakers’b Bakers’b Bakers’ Bakers’

Ita BRILLIANCE

SCORE

94 .8 93 .7 93 .4 92 .8 92 .8 92 .7 92 .7 91 .8 91 .6 91 .4 91 .3 90 .9 90 .7 90 .5 90 .5 90 .5 90 .2 89 .4 89 .4 89 .4 89 .1 88 .8 88 .8 88 .2 88 .0 87 .7 87 .6 87 .4 87 .4 85 .8

Y ~ L L O W SCORE

3 . 8 5 . 6 6 . 3 6 . 2

11 .3 4 . 5

11 .0 6 . 4 6 . 0 5 . 8

14.2 5 . 8

12 .5 6 . 2 7 . 2

13 .9 6 . 9 9 . 5 6 . 4 8 . 4 8 . 9 6 . 0

13 .7 8 . 5 8 . 3 8 . 3 9 . 8

11 .6 9 . 8 7 . 6

a 15 per cent moisture basis. b Unbleached.

Although curves were run on the other samples, the results were not included because the data as to ash or moisture content were incomplete. These samples were classified into patent, straight, and bakers’ grade according to the miller’s designation when that was furnished, or according to the recommendation of Alway and Clark when the miller’s desig- nation was lacking.

It will be seen from this table that the brilliance score tends to decrease with an increasing ash content and the yellow score to increase. This is better illustrated by Figures 3 and 4. It is expected that more work along this line will be under- taken when a commercial model of the color analyzer is available for routine purposes.

,

Rapid Calibration of Pipets and Burets’ Alfred T. Shohl

BABIES’ AND CHILDREN’S HOSPITAL, DEPARTMENT OF PEDIATRICS OF SCHOOL OF MEDICINE, WESTERN RESERVE UNIVERSITY, CLEVELAND, OHIO

HE method proposed is rapid and accurate and invdlves no special apparatus. It depends upon the specific T gravity of mercury. The required weights and one of a

pair of tared flasks are placed upon the right pan of a rough balance. The other tared flask is placed upon the left pan. Mercury, covered by a layer of water, is deIivered from the apparatus to be calibrated into the second flask until the balance just turns. Delivery of the known weight of mercury measures the desired volume.

The upper graduation is first marked and etched. A narrow strip of paper is then gummed lengthwise along the lower stem at the point where the lower calibration is to be made, and a stopcock attached to the tip of the pipet with heavy-walled rubber tubing. Into the pipet is introduced, by suction, first a little water and then mercury to a point somewhat above the upper mark. The stopcock is manipulated so that the water meniscus is on the etched line. The delivery time is recorded and a mark made upon the gummed paper at the lowest

The pipet must be standardized between marks.

1 Received December 7, 1928.

point of the water meniscus. The mark is then permanently etched.

Burets and Mohr pipets are calibrated in the same fashion. The method has been used to check calibrations etched by the manufacturers.

When the water delivered from a pipet is weighed and the mark ascertained by trial and error according to the usual method, 1 hour is required to calibrate each pipet. The first time the above method was used, with no effort to attain speed, twelve pipets were calibrated in 1 hour. The correct weights are a t once placed upon the balance. The mercury is poured out after each determination and leaves the flask dry and clean. This eliminates re-weighing the flask, or cleaning and drying it between determinations. Further, since the exact weight is already on the balance pan, the calibration is correct a t the first trial. If too much mercury is delivered, a few drops can be withdrawn from the weighing flask with a hypodermic syringe and needle and returned quantitatively to the apparatus.

The accuracy of the method was tested by the weight of

July 15, 1929 INDUXTRIAL A N D ENGINEERING CHEMISTRY 153

water delivered. In every case it came within the limits given by Treadwell (3) and the Bureau of Standards (1). For 5-ml. pipets the error ran from 0.0 to 0.3 per cent. It is consider- ably easier to attain a given accuracy with mercury than with water, because of the former's greater specific gravity and sur- face tension. An ordinary buret stopcock will deliver a drop of the order of 100 mg. of mercury, which is equivalent to 0.007-0.008 ml. of water. By the use of a Luer adapter and hypodermic needle a drop of mercury of 5-10 mg. may be delivered (2) . Hence for a 1-ml. pipet a balance with a sensi- tivity of 50 mg. is accurate, and for a 100-ml. pipet one with a 500 mg. sensitivity may be used.

The position of the balance when the weighing flask was visibly heavy has been chosen as the end point and the tared flask thus adjusted. It is equally satisfactory to balance the

tares and subtract from the weights added the amount neces- sary to turn the balance.

As with the Ostwald calibrating pipet, by this method the required amount is delivered directly. The Ostwald method involves a calibration of the calibrating instrument; the pipet should be fitted with a three-way stopcock and made to contain exactly the desired amount. The method sug- gested has been found to be as accurate and more conven- ient.

Literature Cited

(1) Bur. Standards, Circ. 9 (1916). (2) Shohl, J. Am. Chem. Soc., 50, 417 (1928). (3) Treadwell, "Analytical Chemistry. Vol. 11-Quantitative Analysis," p.

522 (1919).

Large-Capacity Laboratory Condensers' D. F. Othmer

EASTMAN KODAE COMPANY, ROCHESTER, N. Y.

N THE operation of several glass distillation units used for the preparation of small amounts of fine chemicals I and for distillation studies, glass condensers of a greater

capacity than those ordinarily found in laboratories were necessary. Two types have been developed and their use- fulness proved on dozens of operations.2

Figure 1 shows a double-coil condenser with water flowing in both tubes in parallel and vapors condensing on both coils and to a smaller extent on the inner wall of the jacket due to the cooling of the air. Single-coil condensers of this type are also in use, but when a compact unit is necessary the double coil is recommended. In many set-ups where a liquid seal is necessary on the outlet, a vent tube is inserted through the top stopper carrying the vapor inlet and ex- tended along the axis till it touches the bottom coil.

The advantages of this type of condenser over the numerous other kinds which have been used in this laboratory are:

(1) It offers the maximum amount of effective cooling surface in the minimum space. The head room necessary for a laboratory distillation unit is usually considerably reduced.

(2) There is no back pressure or tendency to prime as in the usual coil condenser.

(3) Only one-tenth to one-half as much water is required, since it may usually be discharged within 10" C. of the tempera- ture of the vapor. (4) When only a constant predetermined fraction of the

vapors is to be condensed-as, for example, in a dephlegmator condenser-changes may quickly be made, since the water hold- up is very small and the control is much more reliable as the uncertainty of convection currents is eliminated.

Relative dimensions vary with the use for which the condenser is intended and those of the one shown are merely suggestive: length over all 330 mm.; outside diameter of jacket 68 mm., of tubing in outer coil 8 mm., in inner coil 6 mm., of vapor inlet 30 mm., and of condensate outlet 10 mm .

The size of the condenser described above is limited by the size of the jacket which can be fabricated, and a condenser of still larger capacity is indicated in Figure 2. In this unit the vapors are condensed inside the coils as in the ordi- nary coil condenser. Such a condenser usually has a great

1 Received April 12, 1929. 2 These condensers have been satisfactorily constructed and are

available in different sizes from the Technical Glass Co., Rochester, N. Y.

length of cooling coil of very small bore, and consequently all the vapors which can enter are cooled in the first few turns and the remainder of the length is wasted. To utilize the whole area, the condenser shown has a coil short in com- parison to the bore and consists of two individual helixes screwed together and welded top and bottom. The cross section of the vapor inlet a t the neck is slightly larger than the sum of the cross sections of the two coils.

A sheet metal can is formed of a tube with bottom and half of a standard 1-inch I. P. S. coupling soldered on. The can and coil are assembled with a rubber stopper as shown.

The dimensions of this particular condenser are: over-all length 410 mm.; outside diameter 85 mm., of tube 10 mm., of inlet 28 mm., and of outlet 10 mm.

Figure 1

U Figure 2