Mechanical Science, 461 



March, 1822. The prize of fifty ducats will be adjudged at 

 the public setting, on the anniversary of Leibnitz, on the 3rd 

 of July following. 



II. Chemical Science. 



§ Chemistry. 



1 . On the Application of Chromate of Lead to Silk, Wool, Linen, 

 and Cotton, hif M. J. L. Lassaigne. — The colouring matters fixed 

 on these substances were formerly obtained from organic bodies. 

 Mineral substances, so abundant in unalterable coloured com- 

 binations, give none to the dyer. It is only within these last 

 few years that mineral preparations have been applied in dyeing. 

 M. Raymond of Lyons is the first, who, by a simple and in- 

 genious process, fixed Prussian blue on silk ; and last year, 

 M. Braconnot of Nancy, by applying the sulphuret of arsenic 

 to cloth, ^c, furnished a yellow colour not less durable. 



In the course of some experiments on the chromate of lead, 

 I succeeded by an analogous process to that of M. Raymond, 

 in combining this salt with all the substances mentioned above. 

 Skeins of silk were placed at the common temperature in a 

 weak solution of sub-acetate of lead for a quarter of an hour, 

 and then removed and washed in abundance of water. These 

 skeins were then put into a weak solution of neutral chromate 

 of potash ', they immediately became of a fine yellow colour, 

 which increased for ten minutes. When they had obtained the 

 maximum of colour, they were taken out, washed and dried. 



This colour is unalterable in the air. By varying the pro- 

 portions of sub-acetate of lead and chromate of potash, various 

 tints may be produced. 



The same process succeeds with wool, cotton, and linen, but 

 it is better to place these substsmces in a solution of sub- 

 acetate of lead, raised to the temperature of 5b^ or 60°. 

 (130° to 140° F.) 



The circumstance that this, like the other mineral colours, 

 is in part decomposed by soap, induces me to suppose that it 

 will only be useful in dyeing silk. 



