114 POISONS : THEIR EFFECTS AND DETECTION. [§§ 86-88. 
Pure nitric acid has a specific gravity of 1-52, and boils at 98°. Dr 
Ure examined the boiling-point and other properties of nitric acid very 
fully. An acid of 1-5 specific gravity boils at 98-8° ; of specific gravity 
1-45, at 115-5°; of specific gravity 1-40, at 118-8°; of specific gravity 1-42, 
at 122-8°, 123°-124°. The acid of specific gravity 1-42 is the standard 
acid of the British Pharmacopoeia. It can always be obtained by 
distilling either strong or moderately weak nitric acid ; for, on the one 
hand, the acid on distillation gets weaker until the gravity of 1-42 is 
reached, or, on the other, it becomes stronger. 
It has been held that acid of 1-42 gravity is a definite hydrate, 
(2N0 3 H, 3H 2 0) ; it corresponds to 70 per cent, of the liquid acid HN0 3 . 
There are also at least two other hydrates known—one an acid of 1-484 
specific gravity, 2N0 3 H, H 2 0, b.p. 121° ; the other an acid of specific 
gravity 1-405, 4N0 3 H, 7H 2 0, b.p. 125°. 
In Germany the official acid is of 1-185 specific gravity, correspond¬ 
ing to about 30 per cent, of HN0 3 . The dilute nitric acid of the Phar¬ 
macopoeia is a colourless liquid, of specific gravity 1-057, and should 
contain about 10 per cent, of acid. The acids used in various industries 
are known respectively as dyers’ and engravers’ acid. Dyers’ acid has a 
specific gravity of 1-33 to 1-34 (66° to 68° Twad.), that is, strength 
from 56 to 58 per cent, of HN0 3 . Engravers' acid is stronger, being of 
1-40 specific gravity (80° Twad.), and contains 70 per cent, of HN0 3 . 
Although the pure acid of commerce is (and should be) almost colourless, 
most commercial specimens are of hues from yellow up to deep red. 
An acid saturated with red oxides of nitrogen is often known as “ fuming 
nitric acid.” 
§ 86. Use in the Arts. —Nitric acid is employed very extensively in 
the arts and manufactures. The dyer uses it as a solvent for tin in the 
preparation of valuable mordants for calico and other fabrics ; the 
engraver uses it for etching copper. It is an indispensable agent in the 
manufacture of gun-cotton, nitro-glycerin, picric acid, and sulphuric 
acid ; it is also used in the manufacture of tallow, in preparing the felt 
for hats, and in the gilding trades. It is said to be utilised to make 
yellowish or fawn-coloured spots on cigar leaves, so as to give them the 
appearance of age and quality. It is also used as a medicine. 
§ 87. Statistics of Poisoning by Nitric Acid.— In the five years 
ending 1916 the acid caused accidentally 16 deaths, and was used in 13 
cases of suicide. 
§ 88. Fatal Dose. —The dose which causes death has not been ascer¬ 
tained with any exactness. As in the case of sulphuric acid, we may go 
so far as to say that it is possible for a few drops of the strong acid 
to be fatal, for, if brought into contact with the vocal* apparatus, fatal 
spasm of the glottis might be excited. The smallest dose on record is 
i'7 grms. (2 drachms), which killed a child aged 13. 
