380 Miscellaneous Intelligence. 



106° and 74°. Each prism was terminated by a dihedral sum- 

 mit formed by two faces proceeding from the narrow faces of 

 the prism, and meeting at an angle of 130°. They did not 

 change by exposure to air. Their taste was sweet, like common 

 acetate of lead. Their specific gravity 2.575. At 60° 100 parts 

 of water dissolved 34.8 of the salt. 



When analysed, it gave Acetic acid 22 



Protoxide of lead .... 59 

 Water 19 



100 

 And Dr. Thomson considers its atomic composition to be five 

 atoms oxide of lead, four atoms acetic acid, and 19 atoms of 

 water. — Annals xiv. p. 382. 



15. Purple Colour for Oil-painting. — His Excellency the Count 

 le Maistre, of St. Petersburg, has, in a letter to Dr. Crichton, 

 described a method of obtaining the above colour, of a fine tint, 

 durable nature, and fit for oil-painting. After noticing the ten- 

 dency muriate of gold has to form purple coloured compounds, as 

 with the oxide of tin in the purple of Cassius ; with gelatine and 

 starch, when mixed and boiled with them ; and with the earths, 

 if precipitated with them, and the precipitates heated ; the fol- 

 lowing directions are given as the best for the preparation of 

 the colour. One part of dry muriate of alumina, one part of 

 sulphate of magnesia, four parts of muriate of barytes, and five 

 parts of carbonate of soda, are each pulverized separately. The 

 pounded salts are mixed in a glass mortar, and a little water is 

 added, merely enough to moisten the mixture. Then a diluted 

 solution of gold is added, by little and little, pounding the 

 matter all the time in the mortar, till the whole has acquired a 

 light sulphur yellow tint, and the consistence of cream. The 

 pounding is continued a long time, to produce the decomposi- 

 tion of the salts with as little water as possible. When no 

 more effervescence is perceptible, and when the salts cease 

 to creak under the pestle, a sufficient quantity of water is 

 to be added for their complete solution. This tedious pro- 

 cess is essential to unite the oxide of gold with the earths ; 



