On Liquid Transpiration in relation to Chemical Composition. 239 



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,.-f-3HO, having sp. gr. 1*4, possesses the highest 

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

 I have elsewhere spoken of as the " constitutional" hydrate of nitric 

 acid. 



In acetic acid, the constitutional hydrate, C 4 H 4 4 + 2 HO, is indi- 

 cated by transpiration with equal precision. The transpiration time 

 rises from 1-2801, the time of the basic hydrate, C 4 H 4 4 , to 

 2*7040, the time of the hydrate first referred to ; falling again after- 

 wards as the water is increased. Butyric and valerianic acids present 

 the same character, although slightly modified. Formic acid, on the 

 other hand, departs entirely from the acetic type in transpirability, as 

 it does in the density of its combinations with water, and in its indis- 

 position to form basic salts. It is curious that liquid formic acid, 

 although an acetic acid by derivation, should more resemble hydro- 

 chloric acid in physical characters. 



The transpiration time of sulphuric acid is 21*6514, a high number, 

 as might be expected from the viscosity of the liquid. But the time 

 rose still further with the addition of water, till 17*5 parts of water 

 were added to 100 of oil of vitriol, when the number was 23*7706. 

 The proportion of water stated approaches closely to 18*36 parts, 

 which represent 1 equivalent. Here again a well-known constitutional 

 hydrate is indicated, SH0 4 + HO. 



In hydrochloric acid the only sensible retardation observed was 

 with the hydrate represented by HC1+ 12 HO. This is the hydrate 

 which possesses least volatility at the low temperature of the expe- 

 riment (20° C). 



It was supposed that glycerine, as a triatomic alcohol, might affect 

 combination with water in the proportion C 6 H 8 6 -f 18 HO. But no 

 such compound was indicated by transpiration of the aqueous solu- 

 tions of glycerine. 



The transpiration of pure acetone is remarkably rapid, and is greatly 

 retarded by the addition of water. The time rises from 0*401, that 

 of anhydrous acetone, to 1*604, the time of the twelve-hydrate, 

 taking the equivalent of acetone as C 6 H 6 2 , or of the six-hydrate 

 with the equivalent C 3 H 3 O. 



The transpiration times and boiling-points of three alcohols are as 

 follows : — 



Transpiration time. Boiling-pont. 



Methylic alcohol 0*630 66° C. 



Vinic alcohol 1*195 78*5 



Amylic alcohol 3*649 132 



