PROGRESS OP CHEMISTRY IN SOUTH LANCASHIRE. 117 



tity of the latter being taken to prevent the watery solution afterwards gela- 

 tinizing. The product has the appearance of glass, transparent in thin 

 layers, and variously coloured in mass, from pale yellow to brown or black, 

 the colour being due to the presence of carbon. Occasionally it is of a pale 

 green. As it is difficult to reduce it into fragments by pounding, on account 

 of its extreme brittleness, it is found advantageous to allow the fused mass 

 to run directly into water, by which means it is immediately broken up into 

 pieces of a convenient size. About 10 tons per week are produced in this 

 neighbourhood. 



VII. Arseniate of Soda. 



This salt has of late come into very general use as a substitute for cow- 

 dung in calico-printing, for which purpose it is much better adapted than 

 the phosphate or silicate of soda, as it does not attack the alumina mordants 

 to so great an extent as those salts. It is generally prepared by fusing 

 arsenious acid with nitrate of soda and caustic soda. Without the addition 

 of caustic soda, an acid arseniate would be formed. In this way, however, 

 a considerable loss of arsenious acid takes place. Mr. Higgin, of this city, 

 has therefore invented and patented a process, by which this loss is prevented. 

 He dissolves the arsenious acid in caustic soda, adds nitrate of soda, introduces 

 the mixture into a reverberatory furnace, and allows the heat of the fire to 

 pass over the surface. In the first instance ammonia is given off, then nitric 

 oxide. The heating is continued until the paste is perfectly dry. This pro- 

 cess is attended by a saving, not only of arsenious acid, but also of nitrate 

 of soda. The advantages attending the use of arseniate of soda for dung- 

 ing are, that a greater proportion of the mordants becomes fixed, and that 

 the colours are superior and the whites purer after dyeing than with other 

 materials. Its use is also attended with greater economy. It is to be re- 

 gretted that so valuable a substance as this should also be one of so highly 

 poisonous a nature. 



The quantity produced in this district amounts to 10 or 12 tons per week. 



VIII. Bichromate of Potash. 



We have nothing new to report regarding the manufacture of this salt. 

 About 14 tons are produced weekly in our district. 



IX. Prussiates of Potash. 



From 4 to 5 tons of yellow prussiate of potash and 1 ton of red prussiate 

 are produced in this district per week. 



X. Superphosphate of Lime. 

 Weekly production in this district, 500 to 600 tons. 



XL Sulphate of Baryta. 



Of this salt, which is usually sold under the name of " blanc fixe," about 

 2 tons are made in this district by precipitation. The plan pursued is very 

 simple : Derbyshire heavy spar is heated with carbon, the sulphide of 

 barium thus obtained is decomposed with muriatic acid, and from the solution 

 the baryta is precipitated as sulphate. When prepared in this manner, it is 

 found to be better adapted for the purpose to which it is applied than the ore 

 simply ground, as it possesses more body as a paint than the latter. 



XII. Epsom Salts. 

 Weekly production in this district, 20 tons. 



