AQUA AMMONIAS.

167

in the United States and Edinburgh Pharmacopoeias . In the DublinPharmacopoeia it is called aqua ammonia caustica. It has also beentermed spiritus salis ammoniaci causticus, cum calce viva paratus.

Preparation. — (a.) In the London Pharmacopoeia it is prepared fromten ounces of hydrochlorate of ammonia, eight ounces of lime, and twopints of water. The lime, slacked with water, is to be first put into aretort, and then the hydrochlorate of ammonia broken into small pieces :the remainder of the water is then to be added, and fifteen fluid ouncesof the solution of ammonia distilled.

The theory of the process is the same as that for making ammoniacal gasjust described. The equivalent proportions of hydrochlorate of ammoniaand lime are 54 of the first and 28 of the latter. Now it is obvious thatmore lime is employed in the process of the London Pharmacopoeia than istheoretically necessary, if the ingredients were pure. Yet in some otherpharmacopoeias the quantity is considerably greater. Thus in that ofDublin the proportions are three parts of hydrochlorate, two parts of lime,and ten partsof water. In the Edinburgh anuUnited States Pharmacopoeias the quantities are, a pound of hydroclilorate, a pound and a half of lime,a pint (or pound) of distilled water, and nine ounces of distilled water.The distilled water is placed in the receiver to absorb the gas. The advan-tage contended for by using this great excess of lime is the facility withwhich the ammonia is disengaged: but this is more than compensated inthe Edinburgh and United States processes by the inconvenient bulk of theingredients. Some excess is of course necessary to allow for impurities.

(h.) In commerce, the impure sulphate of ammonia is frequently substi-tuted for the hydrochlorate. The apparatus employed is an iron cylinderconnected with the ordinary worm refrigerator, and this with a row ofdouble-necked stone-ware bottles containing water, analogous to thosedescribed under the head of nitric acid (see Nitric Acid ).

Properties. —Solution of ammonia is a colourless liquid, having avery pungent odour, and a caustic alkaline taste. Its action on turmericpaper and violet juice is like that of ammoniacal gas before described.It is lighter than water, but its sp. gr. varies with its strength. In theshops a very strong solution (called Liquor ammonia fortior) is kept, havinga sp. gr. 0'880 : it is employed for smelling-bottles. Prepared accordingto the London Pharmacopoeia, the sp. gr. of the water of ammonia is O'900;according to the Dublin, 0'905; according to the United States , 0'944;and according to the Edinburgh , 0'939. The quantity of ammoniacalgas which water can dissolve varies with the pressure of the atmosphereand the temperature of the water.

Davy ( Elements of Chem. Phil. p. 268) ascertained that at the tempe-rature of 50°, under a pressure equal to 29'8 inches, water absorbs about670 times its volume of gas, and becomes of sp. gr. 0'875. He drew upthe following table, shewing the quantity of ammonia in solutions of dif-ferent specific gravities:—

100 parts of Sp. Gr. Of Ammonia.

0-8750 .

0-8875 .

.29-25

0-9000 .

.26-00

0-9054 .

..25-37

0-9166 .

.22-07

0-9255 .

.19-54

0-9.826.

.17-52

0-9385 .

100 parts of Sp. Gr.

Of Ammonia,

0-9435 .

. contain 14-53

0-9476 .

.13-46

0-9513 .......

.12-40

0-9545 .

.11-56

0-9573 .

.10-82

0-9597 .

.1017

0-9619 .

. 9-60

0-9692 .

. 9-50