Miscellanies.- 195 



is that of agitation for some time in water, in a well corked bottle ; 

 but, he observes, the powder obtained by this method is very imper- 

 fect ; whereas if alcohol at 36° be used instead of water, a powder of 

 the utmost fineness is produced, which has a crystalline appearance, 

 and on agitating the liquid in the sun, the bottle appears to be entirely 

 filled with a light brilliant powder. — Ide?n. 



21. Preparation of Sugar from Starch. — M. Heinrich says, that 

 from one to two parts of sulphuric acid for each 100 parts of potato 

 starch is sufficient, if the heat applied be a few degrees above 212 

 Fahr. ; and also, that then tAvo or three hours are sufficient to give 

 crystallizable sugar. He applies the heat in wooden vessels by means 

 of steam, — (Roy. Institution Jour. June, 1830.) — Idem. 



22. Sulphate of Potash and Copper. — When equal quantities of 

 Sulphate of potash and sulphate of copper are mixed, a particularly 

 bright, green precipitate is gradually formed, which Vogel considered 

 as a subsalt. Having been analysed by Brunner, it appears to con- 

 sist of 



Oxide of Copper, ....-- 39.23 



Potash, ^ - 12.12 



Sulphuric acid, - - - - - - 39.70 



Water, - - 8.94 



100.00 



Idem. 



23. On improvement in black writing ink ; hy John Bostoch, M. D. 

 F. R. S., &c. — (Transactions of the Society of Arts of London.) — 

 The changes, which tend the most to impair the value of ink, are its 

 moulding, the separation of the black matter from the fluid, and its 

 loss of color, — the black first changing to brown, and at length disap- 

 pearing. The author considers the gallic acid to be the only part of 

 the solution of the gall nut, which is essentially concerned in the pro- 

 duction of permanent black ink, and that the tan, the mucilage, and 

 the extractive matter are the causes of its deterioration. The mould- 

 ing is considered as arising from the mucilage, and the precipitation 

 to be chiefly occasioned by the extractive matter. The tan, it is con- 

 jectured, forms a triple compound, in the first instance, with gallic 

 acid and the iron ; and that in consequence of the decomposition of 

 the tan, this compound is afterwards destroyed. 



The practical conclusions, says the author, that I think myself war- 

 ranted in drawing from these experiments, are as follows : — In order 

 to procure an ink, which may be little disposed either to mould or 



