The oxy-muriatic gas is conveyed by the lead tube G, which is two inches in diameter, into the interme diate vessel H, set upon a stand as in the figure. This vessel is circular, and is from 12 to 18 inches in diameter, according to the capacity of the other parts of the apparatus ; the use of it is to prevent any im purity from descending by the leaden tube I into the receiver K, should the contents of the retort be for ced upwards by the effervescence of the materials in it ; but this is now seldom the case, since the distilla tion of the oxymuriatic acid is carried on by the use of the water bath, in place of heated sand.
The receiver- K is a vessel oft n inverted conical shape made of lead, where the capacity does not ex ceed 120 gallons, or of wood lined with lead when the quantity of work done is large. It is closely covered at top, and has a hole for introducing water into the receiver at M with a leaden plug. The brass stopcock for drawing off the oxymunatic acid, is about two inches from the bottom of the receiver, as at N. In tome apparatus' of this kind, two or three false bottoms, as they are called LL, made of lead, are laid on brackets of the same metal fixed to the side of the receiver. These false bottoms are pierced full of holes, in order to spread the oxy.muriatic gas through the water during the distillation.
.0f the Detergent and other Substances used in Bleaching.
As it is of importance for the bleacher to be ac I quairted with the qualities of the substances he uses, and to know the proper methods of ascertaining their purity, in this Chapter we shall briefly point out the manner of arriving at the knowledge of this. The substances used in bleaching are chiefly, 1. Pot and pearl ashes.
2,. Soda. 3. Soap.
9. Oxy•muriate of potash.
5. Oxy.muriate of lime.
G. Manganese.
7. Muriatic acid.
8. Sulphuric acid.
I. Pot and pearl ashes, as they ir imported from the United States of America; whence the prin cipal supplies are derived, are of three different qua lities : first, second, and third sorts, the casks which contain them being branded by a hot iron with these distinguishing marks. As may naturally be sup posed, the first sort is the best, the second next in quality, and the third sort the worst.
But the best potash, as imported, is by no means an alkali free from impurity, it being only compara tively so when its value is estimated with respect to the inferior kinds. It never contains above 70 per cent. of real alkali, but more frequently from GO to 65 per cent. ; the remainder of the mass consisting of sul phate and muriate of potash, muriate of soda, a por tion of uncombined charcoal, carbonic acid, and five or six per cent. of water. As these substances possess no detergent qualities whatever, it is the interest of the .bleacher to purchase only those kinds of potash which contain the smallest portion of these adventi tious salts. The second tort of potash is often very impure, and the third or lowest quality is frequently designedly mixed with common salt, m order to in crease the weight. The same observations are appli cable to pearl ashes, which differ from potash only in containing a greater proportion of carbonic acid, and consequently are what is termed a milder alkali.
Wilma solution of pot or pearl ashes is made by bleachers, it is customary to ascertain the strength of the solution by the hydrometer, an instrument admi rably calculated for this purpose, were these salts always of the same degree of purity. But as this is not the case, we shall point out two methods whereby this may be ascertained with a sufficient degree of accuracy.
1. It is a fact well known to chemists, that the strength of an alkali is in proportion to the quantity of any acid required to saturate it. Thus, if an ounce of one kind of potash requires for saturation a given quantity of sulphuric acid, and an ounce of another kind of potash requires twice that quantity, the latter is twice as strong as the former.
In order, however, to obtain a sufficiently accurate standard of comparison, it will be necessary always to employ an acid of the same strength. This may be effected sufficiently well for ordinary purposes, by diluting the common sulphuric acid of commerce to the same degree by the hydrometer. For example, let the standard consist of one part of acid and five of water. After the mixture has cooled down to the tem perature of 60 degrees of Fahrenheit's thermometer, observe the height to which the hydrometer rises, and make this the standard for subsequent trials. The strength of an alkali will now be learned, by ob serving what quantity of this acid a given quantity of the alkali under trial' requires for saturation. For this purpose, put half an ounce of the alkali into a jar with a few ounces of water, and filter the solution ; weigh the diluted acid employed before adding it to the alkali ; then pour it gradually into the solution till the effervescence ceases, and till the colour of litmus paper, which has been reddened with vinegar, ceases to be restored to blue. When this happens, the point of saturation will be attained. Weigh the bottle, to know how much rf the acid has been added, and the loss of the weight of the acid NI Ill ascertain the strength of the 2. Another method recommended by Dr Higgins of Dublin, for ascertaining the purity of potash, is, • to take a given quantity of the alkali, and dissolve it in twice its weig' t of boiling water, stirring the mix ture during the solution of the salt ; while yet warm, it must be filtered through unsized paper. When all the liquor has passed through the filter, a very small quantity of cold water is gradually poured on the saline residuum on the filter, in order to wash out the remainder of the alkali. The undissolved salt remain ing on the filter, is sulphate of potash, which must be carefully taken off, dried and weighed, in order to ascertain its quantity. To determine whether any commol1 salt is contained in the alkali which has been filtered, evaporate the clear solution a little in a sand bath, and set it in a cool place for 24 hours ; at the end of which time, any common salt it may contain, will be found crystallized in the form of regular cubes at the bottom of the vessel. The sulphate of potash and common salt being dried, weighed, and deducted from the weight of the crude alkali employed, will give the precise weight of the pure alkali it contains.