1252 INDUSTRIAL A N D ENGINEERING CHEMISTRY Vol. 17, No. 12

are rather strikingly brought out. Curve 1, giving Saybolt viscosity a t 100' F. against boiling point, shows a decrease in viscosity, for the same boiling point, as the naphthenic character of the crude decreases and its paraffinic character increases. Conversely, for the same viscosity the naphthenic crude has the lowest boiling point. This, of course, accords directly with the general experience that the naphthenic crudes give low flash points, the flash in fractions of this kind naturally increasing or decreasing with the boiling point.

I /oo - /+0 /Bo 220 260 JOO 3+0 QBO

5 0 X B O I L I N G POINT BIOmm.-eC.

The fact that the removal of the wax from the Midcontinent crude raises its curve more nearly to the Gulf Coast is due to the concentration of the naphthenic constituents by removal of some of the paraffinic constituents, thus making the crude more naphthenic in character. A few miscellaneous experi- ments, in which the wax was removed fairly completely, brought the Midcontinent curve very neakly up to the Gulf Coast 1 curve. The fact that the removal of wax from the Pennsylvania fractions has little effect on the curve is ex- tremely interesting.

Curve 2, showing the 210" F. viscosity against the boiling point, brings out exactly the same relations as Curve 1, ex- cept that a t the higher temperature the curves are brought closer together, owing to the higher coefficient of viscosity change with temperature in the naphthenic oils. This fact is shown very well by the following data taken from the curves :

60 Per cent Boiling Point of Fraction with: Vis./lOOo F. 1000 Vis./210° F. - 58

0 c. 0 c. Gulf Coast 3 Gulf Coast 2 Gulf Coast 1 Midcontinent Pennsylvania

-.

243 268 303 329 351

~. 243 263 283 293 313

Curve 3, plotting the specific gravities against the 50 per cent boiling points, shows the same relationship between the individual curves except that the differences in gravities are more nearly constant over the range of boiling points. Again the partially dewaxed Midcontinent fractions are brought closer to the Gulf Coast while the part,ially dewaxed Penn-

sylvania fractions show little difference. The same relation- ships are brought out in Curve 4, showing refractive index against boiling point.

Application

The relationships brought out above should find a usefulness in many different ways. For example, it is possible on any given crude definitely to tie up the viscosity with the boiling points of the fractions so that from the vacuum assay dis- tillation of the viscosity oil it is possible to estimate yields of oil of various viscosities in the same way that the yield of naphthas are commonly estimated, by an inspection of the assay distillation of the light cuts. The relationship between boiling point and the other properties should also give con- siderable help in determining the composition of an unknown lubricating blend.

Gallium-in-Quartz Thermometer Graduated to 1000" C.'

By Sylvester Boyer

THOMSON RESBARCE LABORATORY, GENERAL ELScrarc Co., WEST LYNN, MA$%

EMPERATURES much above 700" C. have not here tofore been recorded by direct-reading thermometers. The upper limit of the mercury-in-glass thermometer,

because of the marked hysteresis of glass, is about 500' C. Mercury-in-quartz thermometers reading to about 700" C., using gas pressure for raising the boiling point of the mercury, have been manufactured in Germany in limited numbers. Above this range Dufour2 attempted to substitute tin for mercury, but because of the relatively high freezing point it was not adequate. The range in temperature above the mercury limits has been measured by changing electrical properties of certain metals with changing temperatures. These methods are troublesome, since the apparatus requires frequent rechecking. The first problem, therefore, in the production of a thermometer was the choice of a suitable filling liquid.

The Filling Liquid

Previous work3 on the purification and properties of gallium revealed a number of changing properties with varied treat- ments. More recent investigations on the properties of gallium indicated its possible use as a thermometric liquid. Heretofore the wetting of glass and quartz surfaces by liquid gallium had prohibited its use for this purpose, but the change in this property of the metal was observed when changing the gas pressure above the metal, increasing its purity, removing oxide and water films, and freeing it from absorbed or dis- solved gases. This paper briefly recounts these experimental observations.

T

Properties of Gallium

As reported in the current literature, gallium melts a t 29.7" C. and boils a t approximately 1700' C. It may be undercooled to 1 or 2 degrees above 0" C. before solidifying. The metal, like aluminium, easily becomes coated with sur- face oxides which protect it from further oxidation. Lockyer4 noted that no gas was evolved upon heating in Y ~ C U O .

1 Received October 16, 1926. 2 Burgess-LeChatelier, "High Temperature Measurements," 1911, p.

8 Richards and Boyer, J . Am. Cham. Soc., 43, 274 (1921). 4 Chem. News, 40, 101 (1870).

365.

December, 1925 INDUSTRIAL AND ENGINEERING CHEMISTRY 1253

Lecoq and Jungfleisch' observed that bubbles of gas were evolved when the metal was thrown into hot water.

This investigation relative to using gallium in a high- temperature thermometer added to the knowledge of these properties. When gallium was highly purified and sealed in quartz tubes under 2 or 3 microns pressure, it could be often cooled to - 15' or - 20" C., before becoming solid; but when traces of bismuth were present, it would often solidify a t 3 or 4 degrees above 0" C. and in some cases at room temperature.

When filling the thermometer, oxide a m s which were scarcely observable would increase the tendency of wetting quartz. This oxide forms more easily than one is led to be- lieve from the results previously reported.

The removal of surface oxides was accomplished through treatment with warm dilute hydrochloric acid, and the formation of surface oxidation was prevented during manip- ulation by a surface coating of gallium chlorides and hydro- chloric acid which was later volatilized under vacuum. The usual method of preventing oxidation in an atmosphere of gas was found prohibitive, because gallium absorbed or dissolved gases which were liberated when the thermometer was heated and quickly cooled. Treatment of gallium with halogen gaseq and volatilization of the chloride formed under vacuum also freed the metal from oxide f2ms before use, but the method was not so convenient as the one previously described and therefore was not employed.

Previous to the filling operations the most diffcult variable to control was that of gas removal. Since the metal uoed in this investigation was deposited electrolytically from acid solution, it contained gaseous hydrogen. I n order to remove this gas a large drop of deposited metal was placed in a quartz container under vacuum of 2 to 5 microns and re- peatedly heated to 1100" C. and cooled to room temperature until no more gas bubbles appeared between the metal and walls of the container. The gas liberated appeared to be hydrogen as it did not tarnish the metal. The removal of gas from the metal also added to the brilliancy of its surface.

The tendency to wet quartz because of impurities was also tested. The gallium used contained indium, zinc, and lead, and traces of germanium and arsenic. Lead and indium when added to pure gallium did not increase its tendency to wet quartz, whemas zinc and arsenic did increase its tendency for wetting. It was necessary to remove these elements completely in the purification and by the heat treatment under vacuum.

The Container

A suitable container for thermometry has been made avail- able by the recent progress in the fusing of quartz in this laboratory. Fused quartz capillary tubing of moderately uniform bore can now be produced. Since fused quartz has a very low coefficient of expansion, is transparent, and is subject to but little hysteresis, it has long been known to be an ideal container. The lack of a suitable filling liquid has heretofore prohibited its use for temperatures above the mercury limit.

Method for Filling Container

The metal was freed from oxide by treatment with hydro- chloric acid. When the surface became bright, it was solidi- fied under the acid and the excess acid removed from the surface between filter paper. The surface chlorides pro- tected the metal during transference to the vacuum appa- ratus (Figure 1, a), when the metal was finally heated after a good vacuum had been obtained. The surface coating was thus volatilized, the metal surface became very bright,

BUN. sac. chim., 121 81, 60 (1879).

and the metal assumed the appearance of a globule of mercury. The purified gallium was then introduced into the thermom- eter from the pretreatment chamber. The gas bubbles formed when the metal came in contact with the quartz were finally removed to a chamber (Figure 1, b) containing the reserve of the metal, which was sealed off a t c from the thermometer after the thread was set.

The time of evacuation, temperature, and duration of heating were variable, depending upon the previous history of the metal. I n order to obtain a success- ful thermometer the metal had to be free from oxide, gas, and volatile im- purities. This has all been accomplished and thus gallium has been made an ideal

Marking and Calibration

The marking and calibration of the gallium-in-quartz thermometer pre- sented several new and difficult prob- lems. Quartz is very difficult to etch. With cold hydrofluoric acid the whole surface was attacked, since the usual protective coatings for glass did not pro- tect in case of quartz. It was therefore necessary to find a coating of sufficient protective properties. Polymer ized China wood oil adequately served the purpose. Hot dilute hydrofluoric acid could now be used and the surface of the quartz was protected and the marks were relatively sharp and deep.

The etching of the calibrations alone is satisfactory where accuracy is desired. When less accuracy and greater visibility are demanded, it was found necessary to develop a composition to color the etched marks. After the usual trial samples, it was found that sand and copper oxide in certain proportions would form a sharp grayish black mark, which was re- sistant to most chemical reagents and to heat treatment at 1000" C.

The fixed points on the thermometer scale were determined by comparison with a thermocouple as standard or by direct comparison with certain well- known standards for temperatures. Temperatures in the ranae of 700" C.

liquid f o r high-temperature thermom- eters.

and above presented a greater difficulty as the thermometer had to be protected from the action of the metals, or salts used, and thus giving rise to greater uncertainty as to the degree of accuracy.

A number of these thermometers have been made during the investigation and have functioned satisfactorily. Others have been loaned to various interested parties for further tests.

Acknowledgment

Acknowledgment is made to Berthold Niedergesass for the many valuable suggestions concerning the method of filling and the care of fused quartz, and also to Edward R. Berry for his continued interest in this investigation.

Drawback on Veneer Glue-Latvia has granted the application of Riga exporters for an 85 per cent drawback of the import duty on casein used as glue in manufactured veneer exported by them.