354 RECORD OF SCIENCE FOR 1886. 



arranged for projection with lamp, lens, and scale, a deflection of sev- 

 eral centimeters was obtained. The contact points of tlie dissimilar 

 medals must, of course, be protected from air currents. This may be 

 done with felt. ( Wied. Ann., 1885, xxvi, 334 ; Phil. Mag , January. 1886, 

 V, XXI, 80.) 



Grimaldi has studied the expansion of ethyl oxide at pressures vary- 

 ing from 1 to 25 meters of mercury and at temperatures from 0° to 105°. 

 He tinds that the equation of Avenarius, representing the expansion 

 of liquids at the critical pressure, is true approximately for the expan- 

 sion of ether at various pressures up to this point, provided that at each 

 pressure the different co-efficients are employed. The formula then gives 

 values differing by only about 1 per cent, from the experimental results. 

 (J. Phys., January, 1886, II, v. 29.) 



In consequence of Whipple's communication to the Physical Society 

 of London on testing thermometers down to the melting point of mer- 

 cury, the question was raised as to the uniformity with which this metal 

 contracted between 0° and — 39°. Ayrton and Perry have tested this 

 matter experimentally, compariugthe readings of a njercurial thermome- 

 ter loaned them by Whipple with those of a constant-volume air ther- 

 mometer, both immersed in a bath of frozen mercury which was allowed 

 gradually to become warm. When the results were plotted, they formed 

 a straight line so nearly that the conclusion may be drawn that mer- 

 cury expands as regularly below 0° as above 0°, and that there is no 

 critical point for this substance above its freezing-point, as there is for 

 water. Hence temperatures down to — 39° may be correctly measured 

 by a mercury thermometer the stem of which is graduated for equal 

 volumes. (Nature, April, 1886, xxxiii, 575 ; Phil. Mag., October, 18SG, 

 V, XXII, 325.) 



Roth has proposed to determine fusing points by placing the sub- 

 stance in a tube of glass and immersiug it in sulphuric acid, which is 

 then gradually heated. The apparent temperature of fusion is noted on 

 a thermometer placed in the acid, and a small empirical correction gives 

 the true temperature of fusion. (Ber. Berl. Chem. Ges., July, 1SS6, 

 XIX, 1970.) 



Raoult has investigated the effect of mixing salts in solution upon the 

 temperature at which these solutions congeal. Calling the quotient ob- 

 tained by dividing the actual lowering of the freezing point by the weight 

 of the anhydrous substance dissolved in 100 grams of water the co-ef- 

 ficient of depression, he enunciates the following law : If several sub- 

 stances, without chemical action on each other, are simultaneously dis- 

 solved in 100 grams of water, each substance lowers the freezing point 

 in the ratio of its weight and of the co-efficient of depression which it 

 possesses at the temperature of freezing of the mixture. Again, call- 

 ing the depression which would be produced by a molecule of any sub- 

 stance in 100 grams of water the molecular depression, the author gives 

 the following rule for obtaining its value : Trace the curve of the co- 



