A detailed statement of the various methods of estimation belongs rather to scientific researoh than to a work liko the present. For tho guidance of manufacturers, however, it may be stated that the best method is that of Abel and Bloxam, a modification of Gay-Lussao's charcoal process. Twenty grains of the sample to be valued are weighed off and mixed with 30 grains of powdered resin in a platinum crucible. Eighty grains of chloride of sodium are added and the whole ignited gently until no more vapour comes off. After cooling a little, 25 grains of chlorate of potassium are added, heat is again applied, and gradually increased to redness, so as thoroughly to decom pose the chlorate and fuse the whole mixture. It is then removed, dissolved in hot water, filtered, and washed. A drop or two of litmus solution is added to the solution and the amount of alkali, the earbonato of potassium formed in presence of an excess of carbonaceous matter, determined in the ordinary way with a standard solution of sulphuric acid. The original amount of nitrate is then readily calculated, A rough method depends upon the observation of the temperature at which crystals are deposited from the solution of a sample. Forty parts of the saltpetre are dissolved in 100 parts of water at and the exact point when nitrate crystallizes out is noted. The determination of nitrate present is then read off by tho following table :— It is usual to apply to all methods of estimation the term "refraction." Court.) ing an entirely incorrect description of the ordinary analysis, the name is founded upon an old method proposed by Schwartz, based upon the appearance of the surface of the fused salt when fractured. Pura nitrate is coarsely radiate ; when chloride of sodium is present the structure beeomes less distinct, and with si per cent, of the impurity disappears altogether, except at the edges.
Oxalates of Potassium. Formula, neutral salt crystallize in transparent rhombic prisms containing one atom of water of crystallization, which become ohs luu and anhydrous at It is obtained by dissolving carbonate of potassium in oxalic aid to saturation, concen trating and finally evaporating the solution.
Potassium oxalate is used to some considerable extent in dyeing and printing, as a mild form of oxalic acid. It serves as a discharge, is employed in some steam colours to form oxalate of alumina, and occasionally as a mordant.
The binoxalate, forms colourless rhombic prisms, of a sour taste. This substance is often called "salt of sorrel," from its entering into the constitution of the plant. It also occurs in the Rumex and Oxalis acetosella and in garden rhubarb. It is soluble in about 40 parts of cold and 6 parts of boiling water. Under the name of "salts of lemon" it is largely sold to remove ink and iron stains.
The binoxalate is produced by dissolving oxalic acid in hot water, dividing the solution in two park saturating the one half with potassium carbonate and pouring in the other.
S'ilintte of l'otis,;.iui. (Fa., Silicate de ; GER., es Formula,
This salt forms a peculiar, transparent glass, with a slight green tinge due to the presence of iron. It is slowly soluble in water, forming an alkaline liquid possessed of cleansing properties, and decomposable by nearly all acids with liberation of silicic acid. It is usually manufactured by fusing 45 parts of sand, 3 of charcoal, and 80 of potassium carbonate in an ordinary reverberatory furnace. The carbon dioxide of the carbonate is reduced to oxide by the charcoal and finally driven off. A liquid silicate is made by heating the solid " glass" in powder with superheated steam in a close vessel. A thick fluid, specific gravity about 1.3, is formed, to which is often added silicate of soda solution.
On account of their cleansing properties, the silicates are used for mixing with soaps. For this purpose the mixed silicates of sodium and potassium are, however, chiefly employed.
Sulphate of Potassium. (FR., Sulfate de Potasse ; GER., Schtoefelsaures Kali.) Formula, K2SO4 —This salt occurs in nature in considerable quantities, in various minerals, and in the ashes of both marine and land plants. In the Stassfurth and Kalutz mines it is found in combination with sulphate and chloride of magnesium, forming the mineral kainit.
Sulphate of potassium forms hard, colourless, anhydrous crystals, insoluble altogether in alcohol and soluble in about 10 parts of water. The solubility increases slightly with an increase of temperature. Thus 100 parts of water dissolve : — Sulphate of potassium has a bitter, saline taste, and is neutral to test paper. The crystals decrepitate when suddenly heated, owing to the presence of a small quantity of mother liquor.
The usual method of manufacture is to decompose chloride of potassium with sulphuric acid, the process being almost exactly similar to the Le Blanc sulphate of soda process, to which further and detailed reference will be. made hereafter. It may be mentioned that the decomposition of the potassium chloride, on account of the smallness and irregularity of the grain, requires the aid of mechanical contrivances even more than common salt. Large quantities of sulphate of potassium are also made from kelp, and as a bye-product in the treatment of beet-root molasses for carbonate of potash. Tho product of the kelp liquors is a peculiar, pasty substance which has to be dissolved in hot water, concentrated to about 48° Tw., and crystallized in order to get a useful article.
Plate sulphate is a term often applied to this article. The sulphate manufactured from molasses and " suint" is a much purer salt ; so also is the product of the decomposition of chloride of potassium by sulphuric acid. The following table gives the composition of average samples The beet-root sulphate usually contains also traces of the carbonates of potassium and sodium. It is, however, a very good article as a rule ; about 2000 tons per annum are produced hy this method upon the Continent.