SCIENCE. 



[N. S. Vol. VIII. No. 183. 



bable, therefore, that the remarkable prop- 

 erties of liquid hydrogen predicted by 

 theory will prove to be susceptible of ex- 

 planation when they are compared with 

 those of liquid air, volume for volume, at 

 corresponding temperatures as defined by 

 van der Waals. 



James Dewae. 

 EoYAL Institution, London. 



THE SPECIFIC HEAT OF 3IETALS AT LOW 

 TEMPERATURES. 



Dr. Wolcott Gibbs having requested 

 Professor Eood to make some determina- 

 tions of the specific heat of a few metals, 

 employing liquid air, the matter was finally 

 handed over to me by Professor Eood, and 

 I herewith give a short account of the 

 method used and the results obtained. 



Few experiments on the specific heat of 

 substances at low temperatures have been 

 made. The chief cause of this has been the 

 difi&cultj' experienced heretofore in reduc- 

 ing the temperature of bodies to a definite 

 number of degrees sufiBciently below zero, 

 Centigrade. Liquid air affords a means of 

 obtaining a very low temperature, and was 

 procured through the kindness of Mr. 

 Charles E. Tripler, who has devised ap- 

 paratus for making it in considerable quanti- 

 ties. 



In a paper on the liquefaction of gases 

 by Professor Charles Olszewski, in the 

 Philosophical Magazine, London, February, 

 1895, VoL XXXIX., No. CCXXXVIL, pp. 

 188-212, it is stated, that the boiling point 

 of liquefied air under atmospheric pressure 

 is — 191.4°C., that of liquefied nitrogen 

 — 194. 4°C., and that of liquefied oxj'gen 

 — 181. 4°C. These temperatures were deter- 

 mined with a hydrogen thermometer, and 

 are generally accepted as correct. 



Liquefied air changes in composition 

 when in a state of ebullition, ihe percent- 

 age of nitrogen contained in it diminishing, 

 while that of oxygen increases. 



This change occurs because liquid nitro- 

 gen is the more volatile of the two liquid 

 gases, and boils away at a higher rate than 

 liquid oxygen ; consequently liquid air 

 changes in temperature. If it is allowed to 

 boil for a considerable time it becomes al- 

 most pure liquid oxygen and its tempera- 

 ture correspondingly approaches near the 

 boiling point ofthat liquid gas, or — 181. 4°C. 



Such was the case with the liquefied air 

 procured for the experiments on specific 

 heat ; therefore, after standing several 

 hours, the cold liquid employed by me was 

 considered to be liquid oxygen and its tem- 

 perature — 181.4°C. 



A series of determinations were made of 

 the specific heat of copper, iron and alumi- 

 nium between the boiling point of liquid 

 oxygen ( — 181.4°C.) and about 13 degrees 

 Centigrade. 



The method of mixtures was employed 

 and was applied in a manner suggested by 

 Professor Rood. 



The experiments were conducted as fol- 

 lows : 



A piece of metal of known weight was 

 immersed in liquid oxygen (^181. 4°C.); 

 after it had cooled down to the temperature 

 of the liquid, it was lifted out by a silk 

 thread attached to it, and transferred 

 quickly to a calorimeter containing water 

 of known weight and temperature. 



The loss in temperature of the water, due 

 to the insertion of the cold substance, was 

 carefully noted, and the specific heat of the 

 metal computed. 



Various precautions were taken to avoid 

 errors in the results, and the usual correc- 

 tions were applied in the calculations. 



Before the determinations of the specific 

 heat of metals between the boiling point of 

 liquid ox3^gen and normal temperatures 

 (about 13°C.) were begun, a series of ex- 

 periments were performed on the specific 

 heat of copper between 23°C. and the boil- 

 ing point of water (100°C.), under condi- 



