214 Miscellaneous Intelligence, 



acid : for when the sulphuret is dissolved in an alkali, and then 

 mixed with a solution of copper, lead, or iron, the sulphuret forms an 

 insoluble precipitate, in combination with the oxide present. The 

 oxide of lead is the substance which M. Labillardiere has used as 

 his mordant ; the acetate of lead, minj^led with a little acetic acid, 

 and thickened with roasted starch, is printed on the fabric. The 

 bath is made by boiling three ounces of realgar, two ounces of 

 potash, and one of slaked hme, in a pot with water, and being- mo- 

 dified gives various colours. Thus calico, printed with acetate of 

 lead, being immersed cold in this bath, with a certain quantity of 

 ordinary potash, to be ascertained by experience, acquires a red 

 orange colour ; with caustic potash in certain proportions, a reddish 

 brown is obtained; in larger proportion a brown colour is produced, 

 if the temperature be not raised; if heat be apphed, black and 

 many other colours are produced, according to the quantities, the 

 temperature, &c. 



In other cases the cotton has been dyed all over, and then printed 

 upon ; subacetate of lead is the mordant to be used in that case. 

 The method of printing on these colours, which resist mere acids 

 and alkalies, is to print a thickened solution of chromate of pot- 

 ash, and then to pass the w^eb through water acidulated by muria- 

 tic acid ; the printed places become first yellow (chromate of lead), 

 and in a few minutes after white, without any change being pro- 

 duced in the ground colour. — Ann. de V Industrie, i. 178. 



27. Opaque and Transparent IVhite Arsenic. — Relative to the 

 way in which transparent masses of white arsenic become opaque, 

 M. Kruger has made a few experiments, which seem to show that 

 the change depends upon the formation of a hydrate. A tran- 

 sparent piece put under a bell-glass containing air, confined over 

 mercury, underwent no change in appearance or weight. Another 

 piece put into air confined over water became opaque on the sur- 

 face in a few days, and throughout in five weeks ; at first it weighed 

 16.3 grain, and at last 16.4 grains. — Kastner's Archives. — Bull, 

 Univ. A. X. 18. 



28. Reduction of Sulphuret of Arsenic. — Sulphuret of arsenic is 

 occasionally required to be reduced, when in very small quantities, 

 in medico-chemical investigations. Berzelius remarks, that it may 

 frequently be successfully performed, by putting it at the bottom of 

 a small glass-tube, placing a small piece of steel-wire before it, and 

 subliming it over the latter ; the iron takes the sulphur ; the arsenic 

 condenses a little in advance. When the quantities are very small, 

 this process sometimes fails ; then Berzelius recommends the fol- 

 lowing: — The sulphuret is to be introduced into an open quill 

 glass-tube, about four or five inches long, and being held obliquely, 

 thus *^, is to be heated by a spirit-lamp, so that the hottest part 

 shall be a little above the sulphuret, and the vapour be obliged to 



