en KM ISTRY. 271. 



'. i c.c. The whole being put into a flask is placed ha boiling water for an 

 hour. The two liquids are then mixed, and may be used with success when 

 recently prepared. To gild the inside of a glass vessel, a tenth part of its 

 volume must be filled with a mixture formed of two parts of alcohol and one 

 of ether, and then filled with the auriferous solution while still hot ; the vessel 

 must then be placed in water of the temperature of about 176 F. (80 C.) 

 In less than 15 minutes the internal surface will be covered with a pellicle of 

 gold ; the vessel is to be removed when the sides are opaque, or, at any rate, 

 when, seen by transparency, they have assumed a deep green color. The 

 solution of gold is, of course, always reduced by the alcohol ; but if we wi.-ii 

 for a brilliant layer of metallic gold, w T e must arrange so that the affinity of 

 goldjbr water should not be greater than that of gold for glass, and that the 

 latter should be rather stronger than the other. It is difficult to hit upon the 

 exact point, and the least variation in the proportions would injure the results. 

 The above described bath will only gild when recently prepared ; standing for 

 24 hours will destroy this property. "When fit for gilding it possesses a 

 slightly yellow tint ; with time it loses this color, as well as the property of 

 depositing a brilliant layer on glass ; moreover, alcohol then reduces the gold 

 with great difficulty. 



Petitjearis Process. The new process discovered by M. Petitjean for silvering 

 glass is thus described by Prof. Faraday: "It consists essentially in the 

 preparation of a solution containing oxyd of silver, ammonia, nitric and 

 tartaric acids, able to deposit metallic silver either at common or somewhat 

 elevated temperatures. 1540 grams of nitrate of silver being treated with 955 

 grams of strong solution of ammonia, and afterwards with 7700 grains of 

 water, yield a solution to which, when clear, 170 grains of tartaric acid, 

 dissolved in 680 grams of water, are to be added, and then 152 cubic inches 

 more of water, with good agitation. When the liquid has settled, the cleai 

 part is to be poured off; 152 cubic inches of water to be added to the remaining 

 solid matter, that as much may be dissolved as possible, and the clear fluids 

 to be put together and increased by the further addition of 61 cubic inches of 

 water. This is the silvering solution Xo. 1. A second fluid, No. 2, is to be 

 prepared in like manner, with tin's difference, that the tartaric acid is to be 

 doubled hi quantity. 



" The apparatus employed for the silvering of glass plate consists of a cast 

 iron table box, containing water within, and a set of gas burners beneath to 

 heat it. The upper surface of the table is planed and set truly horizontal by 

 a level. Heat is applied until the temperature is 140 Fah. The glass is 

 well cleaned, first with a cloth, after which a plug of cotton, dipped in the 

 silvering fluid and a little polishing powder, is carefully passed over the surface 

 to be silvered, and when this application is dry it is removed by another plug 

 of cotton, and the plate obtained is perfectly clean. The glass is then laid on 

 the table, a portion of the silvering fluid poured on to the surface, and this 

 spread carefully over every part by a cylinder of india rubber stretched upon 

 wood, which has previously been cleaned and wetted with the solution. In 

 this manner a perfect wetting of the surface is obtained, and all air bubbles, 

 &c., are removed. Then more fluid is poured on to the glass until it is 



