374 
IHL. T. GEAHAM ON LIQUID TEANSPIEATION 
capillary ^yas the weight of one atmosphere of 760 millimetres of mercury, and was 
obtained from compressed air contained in a large reservoir provided with a mercurial 
gauge, as in Poiseuille’s experiments. The 
time was noted in seconds which the level of the 
liquid in the bulb took to fall &om the mark c 
to the mark d. This time varied from about 300 
to 900 seconds in different liquids. In successive 
experiments made upon the same liquid, the 
variation in the time, or error of observation, did 
not exceed one or two seconds. The experiment 
was always repeated two or three times, and a 
mean taken. The temperature of the liquid 
transpired was 20° ( 68 ° P.), when not otherwise 
stated. 
The liquid may be introduced into the bulb 
through the open upper tube by means of a tube- 
funnel; but it was found more convenient in prac- 
tice, although requiring a much longer time, to fill 
the bulb by aspiration through the capillary. "With 
this view the compressed air was shut off by a stop- 
cock, and the upper tube of the bulb was then allowed to communicate with the receiver 
of an air-pump, instead, by which exhaustion was produced, while the open end of the 
capillary was immersed in a portion of the liquid. The liquid which entered the bulb 
in this manner was sure to be free from any solid matter which could cause obstruction 
in the capillary during the subsequent passage of the liquid outwards, while the discon- 
necting of the bulb from the rest of the apparatus, for the purpose of filling the former, 
was also avoided. 
Nitric Acid, 
A bulb pro\ided with a capillary tube, distinguished as capillary C, was used in the 
transpiration of nitric acid and of several other liquids. The dimensions of this bulb C 
were as follows : — Capacity of bulb, 8*075 cub. cent. ; length of capillary tube, 28 milhms. ; 
diameter of bore, 0*0942 millim. The time of passage of water through the tube, under 
the pressure of one atmosphere and at the fixed temperature of 20°, was 348 seconds. 
The time of the passage of the most highly concentrated nitric acid through the same 
capillary was found to be 344*5 seconds, or slightly less than the time of water. This 
is the protohydrate of nitric acid, HO . NO 5 or NHOg. With the addition of water to 
the acid, the transpiration of equal volumes of liquid becomes gradually slower ; till as 
much as three additional equivalents of water were added, when the transpiration-time 
rose to its maximum, 732 seconds. The last hydrate is the well-known definite com- 
pound IsHOg-|-3HO, having the specific gravity 1*4, and which possesses the highest 
boiling-point of any compound of nitric acid and water. Diluted beyond this point 
