214 ANNUAL OF SCIENTIFIC DISCOVERY. 



greater proportion of the vapor than the mere blank paper ; so that 

 when, after a few minutes, the engraving is taken out, exposed for a 

 moment or two to the air, and then laid on a film of starch, part of the 

 iodine becomes detached from the engraving, and is transferred to the 

 film of starch, producing a very delicate and beautiful copy of the en- 

 graving. It is necessary to inclose the film of starch between two glass 

 plates in order to preserve it. 



IMPORTANT DISCOVERY IN THE PREPARATION OF PAINT. 



M. LECLAIRE, a somewhat celebrated house-painter of Paris, after 

 a series of difficult and unceasing experiments, has made a very im r 

 portant discovery in the art of mixing paints. It is an undisputed 

 fact, that white lead, which is by far the most important ingredient 

 used in mixing colors, contains an active and very deadly poison, and 

 persons who work with it are often subjected to what is termed the 

 "painters' cholic." The prevalence of this disease is shown by the 

 fact, that, in 1841, 302 persons affected with it were admitted into the 

 hospitals of Paris, of whom 280 were cured, 12 died, and 1 became 

 insane. 



M. Lec.laire's attention having been directed to this subject, after 

 years of labor he has succeeded in discovering a preventative for this 

 disease. To show the problem he had to resolve, we enter somewhat 

 into detail. 



The fundamental colors in painting, those by means of which all 

 possible tints are obtained, are white, black, yellow, red, and blue, 

 and for greater facility green is added; gray is a mixture of black 

 and white, green of yellow and blue, violet and indigo of red and 

 blue, &c. 



The most important of the primitive colors, that which it is the most 

 essential to render perfectly innocuous and unchangeable, is white, 

 which enters into the composition of nearly all paints. The white 

 exclusively employed now is the white oxide or carbonate of lead, of 

 which that called the white of silver is only a more perfect variety. 

 But the oxide of lead is at once a violent poison and eminently subject 

 to decomposition; it becomes dirty and black, and is destroyed by 

 contact with sulphurous vapors, which are so abundant in nature that 

 it is impossible with every imaginable care to protect it from their 

 corroding influence. For the yellow, we have the chromes and the 

 orpines, which, though durable, are very deleterious. The blues and 

 the blacks are at once harmless and durable. The greens are either 

 very expensive, or deleterious, or subject to rapid decomposition. 



All these defects M. Leclaire has supplied. He produces a pure, 

 dazzling, and durable white, by means of the oxide of zinc ; various 

 tints of yellow from the same ; an excellent red, having for its base, sul- 

 phide of antimony ; and a number of fine greens by means of oxide of 

 zinc and sulphate of copper. He also prepares an oil to be used with 

 these paints, which is obtained by boiling lOOlbs. of linseed oil with 

 51bs. of peroxide of manganese. 



Of the complete success of M. Leclaire's paints there is abundant 



