1867,] Chemical Science. 569 



conjunction with Dr. Krackowizcr, formerly of Vienna, at the Lake 

 Major Mines, a quantity of pyrites collected from the tailings (after 

 passing through the mill in the usual way) was re-subjected to the 

 action of mercury, to which sodium had now been added, and by 

 this means the waste material from which all the gold was supposed 

 to have been abstracted, yielded a fresh supply at the rate of five 

 ounces of gold per ton of pyrites. 



In the discussion which followed the reading of this paper, 

 Mr. Crookes said that there was one thing which ought especially 

 to be attended to in employing this process, and that was to avoid 

 introducing too much sodium. Every failure which had come 

 under his notice had arisen from ignorance of the action which the 

 sodium was intended to exert on the mercury. If too much were 

 added it exerted a chemical action, reduced the iron, copper, lead, 

 &c, winch might be present in the ore, and loaded the mercury 

 with base metals, destroying its power of wetting gold, and causing 

 it rapidly to flour away when triturated in a stream of water. If, 

 however, only a trace of sodium were introduced (say 1 in 10,000 

 or 1 in 100,000), it acted physically rather than chemically; it put 

 the mercury into a highly electro-positive state, and by greatly 

 widening the electric interval between this metal and gold, increased 

 their mutual affinity. 



A paper was afterwards read " On certain new Processes in 

 Photography," by J. Spiller. He first described what is known as 

 the "Woodbury-type process, which is based on the insolubility of 

 chromo-gelatin after exposure to light, and upon the subsequent 

 action of water upon a sensitive film, which has been in different 

 degrees influenced by insolation under an ordinary photographic 

 negative. The depths of tint in the original are represented by 

 variations in the thickness of the film of gelatin left unacted upon 

 by water, and this dried may then be used as a matrix to produce 

 a corresponding series of depressions upon a surface of lead or type- 

 metal by the aid of a powerful hydraulic press. The blocks so 

 produced serve for printing off a great number of proofs when they 

 are liberally "inked" with warm gelatin, highly charged with 

 Frankfort black or other suitable pigment, and pressed down upon 

 a smooth sheet of paper until the excess of ink is forced out on all 

 four sides of the block, and so removed from the space constituting 

 the picture, which, when set, is, lastly, protected with a varnish of 

 collodion. A glass plate may be used instead of paper to receive 

 the ink, and this, backed with another (opal) glass, gives an excellent 

 result, suitable for a variety of ornamental purposes. 



Mr. 'Woodbury has lately perfected a modification of his pro- 

 cess, which is applicable to the representation in high relief of 

 microscopic objects. The method consists in spreading a warm 



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