424. Professor Kane on the Action of Ammonia 
The white precipitate, produced by adding water of ammonia to a solution of cor- 
rosive sublimate, is the substance with which we shall commence, as a knowledge of 
its history will be found to facilitate very much the study of those remaining. 
§ 1.—Of the White Precipitate of Mercury. 
It is well known that on adding water of ammonia to a solution of corrosive sub- 
limate, there is obtained a milk-white precipitate, insoluble in water, and possessing 
properties which, as they are made the foundation of many experiments hereafter to 
be described, I shall briefly mention. This precipitate, when first produced, is milk- 
white, very bulky, depositing but slowly, and rather aluminous-looking. If very 
hot water be used in preparing it, or if it be washed very much, it loses its pure white 
colour, and acquires a yellow tinge; if boiled for a few minutes in the liquor, it is 
completely decomposed, and then results a canary-yellow powder, very heavy and 
granular. This white precipitate is perfectly insoluble, as such, in water. An occa- 
sional appearance of solution results from its being decomposed, and one or other of 
its elements entering into new combinations. When heated in a glass tube, sealed at 
one end, it is completely decomposed below a red heat; there is disengaged a mixture 
of ammonia and azote, some water, and calomel sublimes, generally darkened by some 
ammonia, from which, however, it can readily be freed. 
White precipitate dissolves readily in nitric or in muriatic acids ; when mixed with 
an alcali, as potash or soda, or with lime or baryta, there is ammonia disengaged, and 
the mass becomes yellowish, but the decomposition is never complete. ‘The real nature 
of the products we shall hereafter study ; but it may be remarked, that no excess of 
aleali can expel all the ammonia of the body. 
If we add to white precipitate a solution of iodide of potassium, there is deposited 
a red powder, and much ammonia is disengaged. ‘The powder is biniodide of mer- 
cury, and the liquor contains free potash ; all the ammonia is liberated. Sulphuret . 
of barium in solution produces a similar reaction—all the ammonia being disengaged, 
and all the quicksilver deposited as bisulphuret. 
In order to obtain white precipitate of sufficient purity for examination, some precau- 
tions must be observed, the neglect of which has produced much of the confusion in re- 
sults ; different chemists having analyzed heterogeneous products. Toa cold solution of 
bichloride of mercury, there is to be added water of ammonia in very slight excess ; the 
whole is to be thrown on a filter, and as much as possible of the liquor allowed to 
come away before any washing is attempted. It may then be cautiously washed with 
as much distilled water as may suffice to remove the original liquor from the mass, 
but over excess avoided, as, even by cold water, some portions are decomposed, and 
the milk-white colour of the powder lost. 
