318

Preparations and Compositions. Part III.

1*

h

existence in a fluid form. The London college put a portionof water into the receiver, for the purpose of absorbing themuriatic acid gas, which is first disengaged, and which wouldotherwise be lost for want of water to condense it: the othercolleges, however, order the whole of the water to be previ-ously mixed with the sulphuric acid; and it is indispensablynecessary that the mixture of acid and water be allowed tocool before it be added to the salt •, for the heat produced isso great, that it would not only endanger the breaking of theretort, but occasion considerable loss and inconvenience, bythe sudden disengagement of muriatic acid gas. Dr Powellthinks it is an improvement to add the salt to the dilutedacid, but it is less convenient.

Mr Phillips has given us a tabular view of the results ofthe processes of the London pharmacopoeias, 1809 and 1787,and of a modification of the latter.

Mur.soda.

Sulph.acid.

Water.

Cost.

Product.

Sp. gr.

Marbledecomp.

1787 35Modif. 35 '1809 32

212124

17.5

22.

39.4

565656

29.75

35.

43.68

1.188

1.1741.142

15.0916.4317.16

It may be observed, that according to these experiments, thenew process does not produce an acid nearly of the strengthordered by the college, its specific gravity being 1.142 insteadof 1.160, and the nuidounce decomposing only 204 insteadof 220 grains of marble, while muriatic acid from Apotheca-ries Hall is of specific gravity 1.158. The difference ofstrength from the statement in the edition 1809 was great-er, as the sp. gr. was said to be 1.170, and the solvent power240; it may now be accounted for by some variation in themanipulation, especially as Dr Powell quotes the present state-ment as the result of experiment. At any rate, the new pro-cess is more economical, as at a given expence it produces agreater solvent power.

The muriate of soda, which should be of the kind calledBay Salt, is directed by Dublin and Edinburgh to be heat-ed to redness, before it be introduced into the retort, that thewhole of the water of crystallization may be expelled, which,being variable in quantity, would otherwise affect the strengthof the acid produced ; and besides, without this precaution,the acid obtained is too high coloured. The London collegeuse the salt dried, but not decrepitated.

The charge should not occupy more than half the body of