160
ELEMENTS OF MATERIA MEDICA.
heightened by supersaturating with ammonia: powdered nux vomicarenders this acid yellow or orange-coloured. If hydrochloric acid headded to nitric acid, the mixture acquires the power of dissolving leafgold: the presence of gold in solution may be recognized by the proto-chloride of iron, which strikes a purple or dark colour. Lastly, saturatedwith pure carbonate (or bicarbonate) of potash, a nitrate of potash isprocured.
The nitrates are known by the following characters:—they evolveoxygen when heated, and deflagrate when thrown on a red-hotFic. 43. cinder or charcoal; when heated with sulphuricacid they disengage nitric acid, which may berecognized by its action on morphia, brucia, orcommercial strychnia; lastly, when mixed with sul-phuric acid and copper turnings, they generatebinoxide of nitrogen, which is readily recognizedby its blackening a solution of protoxide of iron.This last-mentioned property enables us to recognizevery minute portions of the nitrates. The mixture ofthe nitrate, copper filings, and sulphuric acid is tobe put into the test-tube (fig. 43 a .): adapt, bymeans of a cork, a small curved glass tube, con-taining at the bend ( b) a drop or two of the solu-tion of the protosulphate of iron; apply heat tothe mixture in the test-tube, and in a few mi-nutes the ferruginous solution becomes brown orblackish.
Composition. —Anhydrous or dry nitric acid, such as we find it insome nitrates, has the following composition by weight:
Nitrogen . .Oxygen. . .
Eq.
. 1 .. 5 .
Eq. Wt.
. . 14 . .. . 40 . .
Per Cent.
. . 25 9 .. . 74'1 .
Cavendish.
. . . 25 . .. . . 75 . .
Davy.. 29-5. 70-5
54
100
100
100 .
100
100 -
Its composition by volume is, one volume of nitrogen gas and twoand a half volumes of oxygen gas. The degree ofcondensation, however, is not known, as uncombinedanhydrous nitric acid has not yet been procured.
1 eq.Nitrog.= 14
1 eq.Oxyg.= 8
1 eq.Oxyg.=8
1 eq.Oxyg.= 8
1 eq.Oxyg.= 8
jl eq.Oxyg.
L =s
Liquid nitric acid is composed of nitric acid andwater. According to Mr. Phillips, when the specificgravity of the liquid is 1'5033 to P504, the compo-sition is as follows:
Eq. Eq. Wt. Per Cent.
Dry or Anhydrous Nitric Acid.1 . . .54.80
Sesquihydrate of NitricAcid.1 .. (J7■ 5. \ qq
100 grains of this acid will saturate about 217 grains of carbonateof soda.
The dilute nitric acid of the London Pharmacopoeia is prepared bymixing a fluid ounce of the strong liquid nitric acid with nine fluidounces of distilled water. Its sp. gr. is P080. 100 grains saturate