Tannic acid precipitates solutions of starch, albumen and gluten, and forms with gluten an insoluble compound which is the basis of leather.
Chromic Acid.—To 100 parts, by measure, of cold saturated solution of bichromate of potassa, 150 parts of sulphuric acid are added and allowed to cool; the sulphuric acid unites with the potassa, and the chromic acid crystallized in deep red needles, very soluble and deliquescent.
It is a powerful oxydizing and bleaching agent. Small animals, as mice, etc., after being immersed in the acid were so completely dissolved after 20 minutes, that no traces were left of either their claws, hair, bones or teeth.
Sulphurous Acid.—It is prepared by exposing to heat a mixture of one part concentrated sulphuric acid with one part of mercury, or one-third part of copper filings, washing the gas by passing it through a little water, and condensing it in water which is well cooled. Professor Proctor directs the gas evolved from four ounces of copper turnings, and eight fluid ounces of sulphuric acid, to be condensed into four pints of water.
Sulphurous acid is a gas which dissolves largely in water and has a smell of burning sulphur.
Liquor Chlorinated Soda—Labarraque Disinfecting Solution.—It is prepared as follows:
| Chloride of Lime, | 1 | pound, |
| Carbonate of Soda, | 2 | pounds, |
| Water, | 1½ | gallons. |
Dissolve the carbonate of soda in 3 pints of water by the aid of heat; to the remainder of the water add, by small portions at a time, the chloride of lime, previously well triturated, stirring the mixture after each addition; set the mixture by for several hours that the drugs may subside, then decant the clear liquid and mix it with the solution of carbonate of soda. Lastly, decant the clear liquor from the precipitated carbonate of lime, pass it through a linen cloth and keep it in bottles secluded from the light.
It is a colorless alkaline solution, having a faint odor of chlorine, and an alkaline taste; it owes its antiseptic properties to containing hypoclorous acid which is readily liberated by the addition of even a weak acid and, on exposure to the air, by the absorption of carbonic acid.
One of its principal uses is to purify the air in dissecting rooms and hospitals, in which case it acts by decomposing sulphurated hydrogen, against which gas when inhaled, it is also an antidote.