126 REPORT 1861. 



they had several disadvantages, which restricted their use in practice. They 

 were not permanent, they had little body, and they were gelatinous and con- 

 sequently cracked in drying. These disadvantages have been obviated by 

 Messrs. Roberts, Dale and Co., who employ oxide of tin as a base instead of 

 alumina, and produce lakes which, owing partly to their physical condition, 

 and partly to their chemical composition, possess the requisite degree of per- 

 manency and intensity of colour. The lakes prepared by the above-men- 

 tioned firm are sold to the paper-stainers, who make use of them for the 

 manufacture of a peculiar style of paper, called mock flocks, which form an 

 excellent imitation of true flock papers, and are consequently used in large 

 quantities. 



Messrs. Roberts, Dale and Co.'s process for making a scarlet lake from 

 barwood, which is peculiar, may be here shortly described. The colouring- 

 matter of this wood is very slightly soluble in water. The ground wood is 

 therefore simply treated with boiling water, to which the requisite quantity 

 of precipitated oxide of tin is added. The boiling water dissolves some 

 colouring-matter, which is immediately separated by the oxide of tin, and 

 more colouring-matter then passes into solution to be precipitated as before, 

 the process being continued until the compound acquires the requisite inten- 

 sity of colour, and the wood is exhausted. The whole being now left to 

 repose, the wood, which is heavier than the dyed oxide of tin, sinks to the 

 bottom, leaving the pigment floating in the liquid. The latter is decanted 

 off", passed through fine sieves to separate some woody fibre, and allowed to 

 stand. The lake is deposited, and after being pressed is ready for use. The 

 quantity of this lake manufactured weekly by this firm is 2 tons, and the 

 price 8af. per lb. 



The production of artificial colouring-matters for practical purposes has 

 of late attracted much attention among scientific men and manufacturers. 

 To this class of products belongs Murexide, a body which, as far as we know, 

 does not occur ready-formed in nature. This substance, which was first 

 discovered by Prout, and subsequently examined by Liebig and Wohler, was 

 until very recently unknown out of the laboratory of the chemist. This arose 

 from the circumstance that uric acid, the only known source of murexide, 

 has not until recently been found to occur anywhere in large quantities. 

 The discovery of large beds of guano in various parts of the world has fur- 

 nished us with a material containing a sufficient quantity, however small, of 

 that acid to render the manufacture of murexide on a larger scale practicable ; 

 and it is now prepared in quantities surprising to those who have only seen 

 it made on the small scale in the laboratory. The process pursued may be 

 shortly described as follows : — The guano is first treated with dilute acid, in 

 order to decompose the ammoniacal salts contained in it. The residue left 

 by the acid is treated with caustic soda in order to dissolve the uric acid, and 

 the solution, decanted from the insoluble portion (consisting of phosphates, 

 sand, &c.), is supersaturated with muriatic acid. The precipitated uric acid 

 is filtered off, washed with water, and dried, when it has the appearance of a 

 brownish-white crystalline powder. The next part of the process consists in 

 treating the uric acid with nitric acid. Measured quantities of the latter are 

 poured into pots of about 1 gallon capacity, which stand in water for the 

 purpose of being kept cool. A certain weight of uric acid is then introduced, 

 in small quantities at a time, into each pot — a process which occupies about 

 ten hours. The liquid has now a dark-brown colour, and is generally covered 

 with a crystalline crust, consisting of alloxan and alloxantine. It may be 

 remarked that the process does not succeed well unless both these substances 

 are present — a fact already known from the researches of Liebig and Wohler. 



