its Manufaclure and Uses. 1 1 



rest, a partial separation takes place; the denser tar falls to the 

 bottom; the lighter naphtha floats at the top; the acid, the 

 middle part, from which place it is drawn off: in this state it is 

 a little mixed with portions of naphtha and tar, and is denomi- 

 nated by the manufacturer the black acid, for if it were in this 

 state employed in the manufacture of sugar of lead, it would pro- 

 duce a very discoloured ftrticle. By distillation the acid becomes 

 more concentrated and purified: it is in this stage that portion 

 which is sold to the vinegar makers is saturated with chalk ; the 

 solution drawn off and evaported to dryness is exported in the 

 form of the acetate of lime. For the manufacture of the acetate 

 or sugar of lead, the acetate of lime is put into an iron still ; sul- 

 phuric acid diluted with an equal quantity of water is added, in 

 such a proportion as to leave an excess of sulphuric acid. The 

 acetic acid is distilled, and the sulphate of lime or gypsum, formed 

 in the operation, is left in the still. 



The acid drawn off is subjected to another distillation ; the 

 acid in this state is highly concentrated, and the 100 gallons of 

 liquor produced in the first distillation is reduced to about 30 gal- 

 lons of strong acid. In this state it will dissolve nearly half its 

 weight of litharge, which is added to the vinegar whilst cool ; 

 during its admixture there is an increase of temperature of near 

 60 degrees ; in this stage no heat is employed. If the acid wore 

 warmed, there would not only be a considerable loss from evapo- 

 ration ; but the litharge instead of being dissolved vvould form 

 a hard cake or mass. The manufacturer soon ascertains the point 

 of saturation : he distinguishes by the smell an excess of either 

 acid or litharge. If the mass is too thick to let the impurities 

 subside, as much water is added as is equal to the acid employed; 

 after being well stirred it is left for 24 hours to depurate, then 

 drawn off and boiled down to concentration, which is determined 

 by taking out a small portion in a capsule, and observing whether 

 it solidifies on becoming cool. It is then drawn off into casks 

 holding about G or 7 cwt. In about five or six days it Ijccomes 

 solid, at the end of which time, a hole is made at the top, into 

 which a syphon is introduced, in order to draw off the mother- 

 water from the central part ; it is then broke up, picked, and 

 sorted for the calico printers. 



There being no correct account of this process published, will I 

 hope plead my apology in troubling the Society with the above 

 detail. 



From some experiments which have been made, the purified 

 acid has not been found to answer the same purposes as vinegar 

 in the processes of pickling vegetable matter ; in its pure state 

 it is 80 highly concentrated, as to completely decompose onions, 

 cucumbers, ic. ; nor will it answer by i educing it by admixture 



B 2 of 



