IN EELATION TO CKEMICAX COIMPOSITION. 875 
nitric acid begins to pass more freely, and the transpiration-time approaches again to 
that of water. With the addition of twice its weight of water, or about 7 equivalents, 
the acid passed through the capillary in 472 seconds. 
The experiments made upon nitric acid are recorded in the following Table. It will 
be observed that the retardation is considerable for a certain distance on both sides of 
the maximum point. No unusual retardation appears to occur with the proportions of 
water corresponding to 2 and 4 equivalents. The specific gravity of the acid liquid is 
added in the last column of the Table, whenever that property was observed. 
Table I. — Transpiration of Nitric Acid, at 20° C., by Capillary C*. 
(Transpiration-time of water, 348 seconds.) 
Water added to 100 acid 
Water, 
per cent. 
Transpir 
In seconds. 
ition-time. 
Water =1. 
Specific gravity, 
at 15°. 
0 
0 
344-5 
0-9899 
1-5046 
25-47 
20-38 
692 
1-9885 
1-4358 
28'56 ... 2 eqs. HO 
21-43 
705 
2-0258 
30 
23-07 
712 
2-0459 
40 
28-50 
725 
2-0833 
42-85 ... 3 eqs. HO 
29-99 
732 
2-1034 
1-3978 
45 
31-03 
730 
2-0977 
50 
33-33 
728-5 
2-0919 
1-3816 
55 
35-48 
718 
2-0632 
57-12... 4 eqs. HO 
36-35 
712 
2-0459 
60 
37-50 
709-5 
2-0387 
1-3598 
70 
41-17 
683 
1-9626 
1-3407 
80 
44-44 
661 
1-8994 
1-3239 
90 
47-36 
635-5 
1-8261 
100 
50-00 
593 
1-7040 
1-2943 
200 
66-66 
472 
1-3563 
It appears, then, that a certain hydrate of nitric acid is marked out by its low tran- 
spirability so distinctly, that nitric acid could be identified by that physical property. 
Such a property may prove to be typical of a class of acids to which nitric acid 
belongs. The hydration of nitric acid probably advances by three equivalents at a 
time, NHOg-f-SHO, as it does in the magnesian nitrates, NMOg-j-3HO + 3HO. The 
transpiration of the assumed second hydrate of nitric acid was not made the subject of 
experiment. A certain steadiness is obseiwed in the transpiration of this acid on either 
side of the point of maximum retardation. 
* In the following Tables, the particular capillary employed is in eacli case designated by a particidar 
letter. Capillary C, which was more employed than any other, became reduced in length during the course 
of the experiments, the end being ground off on several occasions on account of the choking of the tube. 
This capdlary is then described as C shortened. It did not seem requisite to give in every case the dimen- 
sions of the bulb and capillary tube, as all the experiments were conducted on the same plan, and the tran- 
spiration of water is in every case given as a standard of comparison. Direct experiments were also made, 
which proved that the transpiration-times were sensibly inversely proportional to the effective pressure 
applied to the liquid, as found by Poiseville ; which indicates that the capillaries offered sufficient resist- 
ance to the passage of the liquid. 
