A L C

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A L C

liquid, from which on the addition of dry sub-carbonat of potash the alcohol separated rapidly.Mr. Brando found by experiments with alcoholand coloured water, that this mode separatedthe spirit almost totally from the mixture,whence it is reasonable to infer that no spiritwhatever is generated by distillation, but onlyexpelled from the fermented liquor.

The subacetate of lead is prepared by boilingtwo parts of sugar of lead with one of finelypowdered litharge, in six parts of water. Itshould be kept carefully excluded from theair which is constantly converting it to insolu-ble carbonat of lead. The effect of this sub-acetate in separating all vegetable matter frominfusions of vegetables has been long noticedby Dr. Bostock and other experimental chemists.

ALCOHOL of SULPHUR. See Sul-phur, Alcohol of.

ALKALI (FIXED.)

Potash and soda prepared from the carbonatsof these alkalies by lime, the caustic alkalinesolution being evaporated to dryness, redis-solved in alcohol, and again dried and heatedto redness, have long been considered as beingin as high a state of purity as can be produced bychemical means. See the Article (Potash)Chem. Did. Vol.II.

But a most important discovery has latelybeen made which affects the results of all theanalyses of the neutral salts with a basis ofpotash or soda, and indeed is peculiarly satis-fcictory, as it explains the anomaly, before un-accountable, of the great difference in the esti-mation of these salts when the experiments aremade with the dry alkaline carbonats or the drycaustic alkali. The discovery is, that the caus-tic fixed alkali prepared with the utmost careand brought to a state of fusion in a red heat,is not the simple alkali, but contains a consi-derable proportion of JVater , which cannot beexpelled by any length of fusion, though itdoes not accompany the alkali when neutralizedwith an acid and again brought to the heat ofignition. Hence if in any analytical experi-ment a given weight of ignited caustic alkali issaturated with an acid, and the entire neutralsalt thence resulting is ignited and weighed,it is obvious that if the caustic alkali employedbe considered as mere alkali, the proportion ofalkali in the neutral salt will be much over-rated, and therefore the quantity of acid re-quired to saturate 100 parts of the alkali willbe estimated much lower than the truth.

This anomaly was very accurately stated and» An. Chim. tom. 68.

its real cause suggested by M. Darcet, in aMemoir read at the French Institute, January,1808. a The experiments of this eminentchemist are (in a few words) the followingSome very pure subcarbonat of soda was pre-pared and saturated with a dilute sulphuricacid, containing exactly a tenth part of a pureconcentrated sulphuric acid of 1.844 sp. gr.This subcarbonat was found by various analysesto consist of 63.61 of water : 16.04 of carbonicacid, and 20.35 of soda. A hundred grammesof this subcarbonat were exactly saturated by347 grammes of the dilute sulphuric acid,equal to 34.7 of the concentrated acid; whichwould give 170.515 of the concentrated acidto saturate 100. of the mere soda in the statein which it exists in the Carbonat . On theother hand 100. grammes of caustic soda pre-pared by alcohol and fused in a silver vessel ata red heat, saturated only 119.6 grammes ofthe sulphuric acid in one experiment, and 122.4in another, making a difference of about 50grammes of acid in the estimated quantity inthe two cases. Hence it must follow that thesoda prepared by alcohol contains only 71 to72 per cent, of real alkali in that state in whichit exists in the carbonat, both salts being equallyignited, and therefore that which has usuallybeen considered as pure soda, is properly IIy-drat of Soda , consisting of about 72 of puresoda and 28 of water.

The next experiments on this subject whichwe shall mention are those of M. BertholletThis eminent philosopher in his Researches onthe Laws of Chemical Affinity, has taken muchpains to determine the respective quantities ofmost of the acids and bases that saturate eachother, and in this enquiry the composition ofsulphat of barytes came under particular consi-deration, as it is a salt very commonly obtainedin analytical experiments, and its insolubilityrenders it a very convenient basis of calculation.

It would appear at first to be a problem ofno great difficulty to determine the elements ofthis salt, and yet the calculations of equallyskilful and accurate chemists varied as muchas to give a difference of from 67 to 75 percent, in the proportion of acid, which is muchtoo great to be accounted for from any of thecommon inaccuracies in chemical experiment.

On further examination M. Berthollet foundthe cause of this difference to be in the barytesused. He and M. Thenard employed barytescrystallized from its aqueous solution, evapo-rated to dryness, and strongly ignited. M.k Mem. d’Arcueil , tom. 2. p. SO