New frigorific Towder. 311 



The following were tlie results of experiments performed on the 

 recent decoction of cochineal : 



Exp. 1. Nitromuriate of tin let fall an abundant precipitate of 

 a beautiful piuk ; the liquor remaining above it was almost co- 

 lourless. 



Exp. 2. Solution of muriate of tin produced scarcely any pre- 

 cipitate : the solution was of a pinkish-scarlet colour. 



Exp. 3. Sulphate of copper occasioned a precipitate which 

 formed slowly of a Mazarine colour : the supernatant liquor re- 

 mained perfectly clear, having a slight tinge of the same hue. 



Exp. 4. Superacetate of lead produced an abundant precipi- 

 tate of a beautiful purple : the liquor above it was as clear and 

 colourless as water. This precipitate forms a most excellent 

 pigment for painting in v/ater-colour. 



Exp. 5. Nitrous acid digested with the decoction occasioned 

 a strong effervescence, and an abundant orange precipitate was 

 formed : the supernatant liquor remained perfectly limpid. This 

 effect resembled the action between the same acid and indigo. 



Exp. 6. Muriatic acid produced scarcely any precipitate. The 

 clear solution was of a beautiful red, but dyed cloih o'lly of a dull 

 scarlet. j 



It would appear from a variety of experiments, that cochinea 

 contains two distinct colouring principles, one red, the othe*" 

 purple : if so, in order to olitain a beautiful scarlet, a method 

 must be discovered of dissolving (without altering its properties) 

 the red colouring matter, which might afterwards be fixed by the 

 usual mordant. I am, sir. 



Your obliged servant, 

 April 7, 1817. A Constant Reader. 



*^* In a preceding page of this Number we have given an 

 article by M, Vau(|uelin on a dye from a new species of lac, 

 which may be useful to our correspondent. 



NEW FRICORIFIC POWDER. 



Professor Leslie, whose philosophical labours and discoveries 

 are well known to our readers, has lately made an important ad- 

 dition to his curious and beautiful discovery of artificial congela- 

 tion. He had found bv his early experiments, that decayed 

 wliinstone, or friable mould, reduced to a gross powder, and 

 dried thoroughly, will exert a power of absorbing moisture 

 scarcely inferior to that of sulphuric acid itself. But circum- 

 stances having lately drawn his attention to this subject, he 

 caused some mouldering fragments of porphvritic trap, gathered 

 from the sides of the magnificent road now forming round the 

 Calton-hill, to be pounded and dried carefully before the fire, in 

 a. bachelor's oven. This powder, being tlirown into a wine de- 

 U 4 canter. 



