Progress of Invention. 157 



tion, to which, when it is poured off the plate two or three drops of 

 a thirty- grain solution of silver are to be added, after which it is to 

 be poured on again. Should it be found that the exposure in the 

 camera has been too short, the development may be continued by a 

 gelatino-iron solution. The fixing is effected in the usual way. 

 The resin is supposed to act mechanically; and employed in this 

 manner, the developer need not be pyrogallic acid. Only double 

 the time required for exposure with a wet plate is necessary when 

 this process is employed, and the pictures obtained by means of it 

 are quite satisfactory. It involves, however, one inconvenience : 

 fogging begins to take place after a certain number of plates have 

 passed through the bath. But the addition of a few drops of am- 

 monia or solution of carbonate of soda, and a few drops of solution 

 of cyanide of potassium, placing for a few moments in the sun, 

 filtering, and slightly acidifying with nitric acid, not only renders 

 the bath as good as before, but suits it admirably for use in the wet 

 process. 



New Bleaching Process. — Until a comparatively recent period 

 the process of bleaching was extremely tedious ; it is still both 

 troublesome and expensive. As it is carrried on to an enormous 

 extent, any improvement in it is a matter of the highest import- 

 ance. It has been greatly simplified by MM. Tessie du Mothay 

 and Rousseau, without being rendered less effective or less generally 

 applicable. The article to be bleached is immersed in a solution of 

 permanganate of soda, which has been rendered slightly acid, and 

 is stirred about in it for a few minutes with a glass rod. It is then 

 plunged into a solution of sulphurous acid, which removes the violet 

 brown oxide of manganese deposited upon it in the first bath. After 

 the successive immersions in the two fluids have been repeated two 

 or three times, it is found to be beautifully white, without its fibres 

 being in the least impaired in strength. In this, as in all the pro- 

 cesses which have been used for bleaching, oxygen is the agent 

 which destroys the colouring matters ; but it is here applied in the 

 form of ozone, which is disengaged from the permanganate by the 

 organic matters. Permanganate of soda, is at present, somewhat 

 costly, but MM. Du Mothay and Rousseau have discovered a 

 method of producing it that is extremely economical. 



Substitute for Sodium Amalgam, in Metallurgical Operations. 

 - — The gold set free in extremely minute particles from crushed 

 quartz, etc., is covered with an inpalpable powder which protects it 

 from the action of the mercury intended for its separation, and thus 

 a considerable amount of gold is lost. In addition to this, the 

 mercury thrown into a state of minute division by the agitation 

 employed, being covered by the same impalpable powder, is in- 

 capable of reuniting : a considerable portion therefore assumes the 

 appearance of a fine powder, and is carried off with the refuse ; and 

 thus a large amount of mercury is wasted. These two sources of 

 loss have caused a great diminution of profits. It was, however, 

 fortunately ascertained that the brilliancy of the mercury is 

 restored, so that it will run together freely, and unite with the gold 

 with the greatest avidity, if a minute quantity of sodium amalgam 



