382 



lents of water (or three equivalents of water with the formula of 

 alcohol taken as C 2 H 3 O 2 ), was the most retarded in transpiration. 

 The rate of transpiration appeared here to depend upon chemical 

 composition, and to afford an indication of it. A new physical pro- 

 perty may thus hecome available, like the hoiling-point and others, 

 for fixing the chemical constitution of substances. The same feature 

 was recognized in methylic alcohol, although the six-hydrate here is 

 not remarkable for condensation of volume ; and the inquiry was then 

 extended to the hydrated acids, and to other substances. The results 

 appear to establish the existence of a relation between transpirability 

 and composition. 



The time of passage of equal volumes of different liquids under the 

 same pressure and at the same temperature, may be termed their 

 transpiration times, and be referred to the time of water as unity. The 

 transpiration of nitric acid, NHO 6 , with and without water, at 20 C. 

 was as follows : 



Water added to 100 Transpiration time 



Nitric acid (NHO,). (water = 1). 



0-9899 



25-47 1-9885 



28-56 (2 equivalents) 2-0258 



30 2-0459 



40 2-0833 



42-85 (3 equivalents) 2-1034 (the maximum). 



45 2-0977 



50 2-0919 



55 2-0632 



57'12 (4 equivalents) 2-0459 



60 2-0387 



70 1-9626 



80 1-8994 



90 1-8261 



100 1-7040 



200 .. 1-3563 



The transpiration time rises with successive additions of water, till 

 the proportion corresponding to three equivalents is reached, when 

 the time is 2-1034, and has attained its maximum. Diluted beyond 

 this point the nitric acid begins to pass more freely, and the trans- 

 piration time approaches again to that of water. The hydrate 

 named, NHO 6 + 3HO, having sp. gr. 1-4, possesses the highest 

 boiling-point, and the character of definite composition. It is what 



