152 Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. Studies with the Liquid Hydrogen and Air Calorimeters. 

 I. Specific Heats;* by Sir James Dewar. — "The calorimeter 

 emplc^ed in the following researches was similar to that described 

 in my paper on ' The Scientific Uses of Liquid Air,'f and in an 

 improved form in Madame Curie's work 'Recherches sur les 

 Substances Radio-Actives,' 2d edition, p. 100. A sketch of the 

 apparatus appears in my paper on 'The Absorption and Thermal 

 Evolution of Gases Occluded in Charcoal at Low Temperatures.'^ 



The arrangement employed consists essentially of a large 

 vacuum vessel capable of holding 2 or 3 liters, into which is 

 inserted a smaller vacuum vessel of 25 to 50 c.c. capacity consti- 

 tuting the calorimeter, the latter being sealed on to a long narrow 

 tube which projects from the mouth of the exterior vessel, in 

 which it is lightly held by a loose packing of cotton wool. A 

 little below the upper end a branch tube is taken off which con- 

 veys the volatilized gas from the calorimeter to the gas receiver. 

 To the extremity of the projecting tube a small test-tube, to hold 

 the portions of substance experimented on, is attached by a short 

 piece of rather wide rubber tubing which forms naturally a mov- 

 able joint that can be bent into any position. With care I have 

 found this valve gives as good results as more elaborate means of 

 securing the dropping of the substances into the calorimeter. A 

 small vacuum vessel containing solid carbonic acid, liquid ethy- 

 lene, liquid air, etc., into which the test-tube is placed, cools the 

 materials to different temperatures below those of the laboratory, 

 or alternatively it may be heated in the vapour of water or other 

 liquids." 



The general constants for liquid gas calorimeters (here omitted) 

 show that " an instrument in which liquid air is used has twice 

 the sensibility of a corresponding one in which liquid ethylene is 

 employed, whereas the substitution of liquid hydrogen for liquid 

 air increases the delicacy of the calorimeter some seven times. 

 It is easy to detect the tranference of 1/50 of a gram-calorie in 

 the liquid air instrument, whilst 1/300 of a gram-calorie can 

 be similarly observed in the liquid hydrogen form of the calori- 

 meter." 



A detailed account is given of the method of use of the instru- 

 ment and also of the various sources of error. Of the experi- 

 ments described the following results were obtained for carbon 

 in the form of diamond and of graphite, and for ice. 



* Extracts from an advanced proof (received from the author) of a paper 

 read June 8, before the Royal Society of London. 

 fProc. Koy. Inst., 1894, Vol. xiv, p. 398. 

 iProc. Eoy. Soc, 1904, vol. lxxiv, p. 123. 



