ON CAST IRON. 1 §5 



.ground of purple violet, or its derivative tints, without per- 

 ceptibly altering this ground, it is necessary, before the 

 blocks with other mordants are applied, to pass the alkanet 

 ground through dilute sulphuric acid, to carry off the alu- 

 niine, that has been left untouched by the colouring parti- 

 cles of the alkanet. The purple and its derivative tints will 

 be reddened a little indeed by the action of the acid, without 

 however being much weakened. 



Linen prepared in the same manner as cotton presents 

 nearly the same colours and tints when dyed with tincture L men ma be 

 of alkanet ; and admits the same variations by means of other dyed with al- 

 colouring drugs, or the acetate of iron. kanet, 



The same may be said of silk properly alumed. It affords anc j silk, 

 very brilliant colours by being passed through tincture of 

 alkanet; which however only gives the silk a muddy tinge, 

 if it be prepared with a solution of tin of any kind, instead but not wit h 

 of being alumed. This shows the little affinity of the SOULOn ° m * 

 oxide of tin for the colouring particles of alkanet, which 

 produce no better effect on linen or cotton, prepared with so- 

 lutions of the salts of tin. 



The same inconvenience would probably take place with 

 wool, which I have not treated with tincture of alkanet : but 

 no doubt it would exhibit nearly the same colours as cotton, 

 linen, or silk, after having been well alumed. 



VIII. 



On Cast Iron; by Professor Proust.* 



VOTRAY and black cast iron afford an aromatic hidrogen, 

 which appears to me to hold in solution a part of the oil that Aromatic hl- 

 _ it- i ■ i • • • t mi • i ■ -i drogeri from 



is formed during their solution in acids. 1 his hidrogen grav am i black 



burns heavily; and its flame is tinged with yellow and green, cast iron. 

 Four inches of this gas, however, burned with eight of 

 oxigen, consumed only two, or no more than pure hidrogen 

 would have done. The residuum did not render lime-water 

 turbid. I suspected, therefore, that the oily particles might 



* Journal de Phisique, vol lxiii, p. 463, December, 1806. 



Vol. XVII.— July, 1807. O have 



