5S0 



BLEACHING. 



Bfcaching. use of the flenses is to prevent the retort from being 

 r~~ compressed out of shape, and thereby preventing its 

 Plate fitting properly. Between the joinings of the mouth 

 LVI. of the retort, loose flax, dipt in white lead, ground 



Jrijf. 4. in oil, is spread equally ; and the whole is firmly 



screwed together. In the top of the cover, a circu- 

 lar hole is made of three inches in diameter, for in- 

 troducing the materials for making the bleaching li-. 

 quor, and cleaning out the retort. The hole is fit- 

 ted with a plug of lead C, which is gently struck 

 into the cover when the apparatus is arranged for 

 working, and is luted with a little soft clay to pre- 

 vent the escape of gas. 



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 ofi 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 oxymuriatic acid, is 

 about two inches from the bottom of the receiver, as 

 at N. In some 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 ga6 

 through the water during the distillation. 



CHAP. II. 



JOf the Detergent and other Substances used in 

 Bleaching. 



Of the <te- As it is of importance for the bleacher to be ac- 

 tergentand quainted with the qualities of the substances he uses, 

 other sub- an( j to k now the proper methods of ascertaining their 

 used^n P 111 "' 1 )'' > n tn ' 8 Chapter we shall briefly point out the 

 bleaching, manner of arriving at the knowledge of this. The 

 substances used in bleaching are chiefly, 



1. Pot and pearl ashes. 



2^ Soda. 



". Soap. 



1. Oxy-muriate of potash. 



. r >. Oxy-muriate of lime. 



(i. Manganese. 



?. Muriatic acid. 



6. Sulphuric acid. t 



Potash. i_ p ot ant j pearl asher, as they al^imported from 



the United States of America,- whence the prin- 

 cipal supplies are derived, are of three different qua- 

 lities : viz. first, second, and third sorts, the casks 



which contain them being branded by a hot iron with Bleaching. 



tiiese 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 6.5 

 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 sort of potash is often very 

 impure, and the third or lowest quality is frequently 

 designedly mixed with common salt, in 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. 



When, a 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 triaf requires for saturation. For 

 this purpose, put half an ounce of the alkali into ajar 

 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 of the acid has been added, 

 and the loss of the weight of the acid will ascertain 

 the strength of the alkali. 



2. Another method recommended by Dr Higgins 

 of Dublin, for ascertaining the pMrity of potash, is, 



