1819.] Le Maistre on a fine. Purple Oil Colour. 361 



rapidly occurred to him on a first view of the subject; and as 

 his only object is to court an investigation of a plan which, if 

 Successful, must tend, in so great a degree, towards the ad- 

 vancement of the interests and happiness of mankind, he 

 sincerely trusts that it will not be deemed altogether undeserving 

 of experiment. 



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Article VII. 



ealDDBu. l . 



Method of making a fine Purple Colour for painting in Oil* 

 By his Excellence the Count Le Maistre, of St. Petersburgh. 



(To Dr. Crichton.) 

 >du> s 

 9fli SIR, St. Petersburgh, May 19, 1819. 



I now send you the details which you requested respecting 

 my experiments on the oxides of gold. My object in making 

 them was to procure an unalterable purple colour, which could 

 be employed in oil painting, and which should be equally beau- 

 tiful with that of the purple of cassius when it is fused on enamel 

 or porcelain. 



Painters have often tried to employ the purple of cassius with 

 oil or with water ; but when mixed with oil, it is destitute of a 

 body, and gives dirty and disagreeable colours. It is used with 

 gum for dark shades, and in the same way as the common lacs 

 mixed with a little black without ever obtaining a purple colour. 



The oxide of gold in its nitro-muriatic solution has a natural 

 disposition to pass to purple. Not only tin gives it that colour, 

 but its combination 'with gelatin, with starch, and with several 

 of the earths, has the same shade of colour. 



If we boil a weak solution of starch with a few drops of the 

 nitromuriate of gold, we obtain a precipitate similar in colour to 

 that of cassius ; but it retains its purple colour only while moist, 

 .and becomes violet when diy. Size (la col/e de gaud legere) 

 mixed in small quantity with the solution of gold becomes 

 purple after being exposed for some days to the air. 



In like manner, a ailute solution of gold mixed with different 

 Earthy salts, and precipitated by carbonate of soda, furnishes 

 Stet'tfclres of the earths and oxide of gold, which become purple 

 when exposed to the requisite degree of heat. 



This is the principle upon which the composition of the new 



colour" is founded. After numerous trials with different kinds of 



f^rjlis arid their mixtures, 1 observed. that the combination of 



^pld.with alumina, when heated sufficiently, gave by far th» 



".n«il")i»1 \<» 



• I am indebted for this Taluable paper to Dr. Crichton, Physician in O/cSufctfy 

 to the Emperor of Russia. 



