Chemistry and Physics. 311 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. The Determination of Cuprous and Cupric Sulphides in 

 Mixtures of the Two. — In the course of an investigation on cop- 

 per sulphide minerals, Eugen" Posnjak, having had occasion 

 to determine the two copper sulphides when mixed together, has 

 worked out an interesting method for this purpose. The reaction 

 between cuprous sulphide and silver salts was known from the 

 results of several investigators to proceed according to the equa- 

 tion Cu 2 S + 4AgN0 3 = Ag 2 S + 2Ag + 2Cu(N0 3 ) 2 . In regard to 

 the reaction between cupric sulphide and silver salts there were 

 conflicting statements, so that this point was settled experiment- 

 ally by the use of very pure natural cupric sulphide (the mineral 

 covellite) and the synthetic compound. It was thus found 

 that the reaction is represented by the following equation : 

 CuS+2AgN0 3 = Ag 2 S + Cu(N0 3 ) 2 . *It was then found that a 6 

 per cent solution of ferric nitrate acting at 10° upon mixtures of 

 silver sulphide and metallic silver showed practically no action 

 upon the sulphide, while it dissolved the metal according to the 

 following equation: Ag + Fe(N0 3 ) 3 = AgN0 3 + Fe(N0 3 ) 2 . As 

 many as 10 known mixtures of the two sulphides of copper were 

 treated with 5 per cent solution of silver nitrate, at first while 

 cold, then for three hours on the water bath, the residues were 

 thoroughly washed, then extracted two or three times with the 

 ferric nitrate solution. From the amounts of silver thus dis- 

 solved and remaining as sulphide the quantities of original 

 cuprous and cupric sulphides were calculated, and the results 

 showed very satisfactory agreements with the knowm composition 

 of the mixtures. — Jour. Amer. Chem. Soc, xxxvi, 2475. 



h. l. w. 



2. Feldspar as a Possible Source of Potash. — A. S. Cushman 

 and G. W. Coggeshall have carried out experiments on a rather 

 large scale, following the principle of the well-known analytical 

 process of J. Lawrence Smith. The ground feldspar is mixed 

 with a small proportion of burnt lime, then moistened with water 

 containing about the theoretical amount of calcium chloride 

 required to convert the potassium of the feldspar into chloride. 

 This moistening causes the mixture to collect into small lumps. 

 The product after drying is burnt in a long rotary furnace of the 

 cement-kiln type by the use of powdered coal and an air blast. 

 The nodules retain their form during the burning and are deliv- 

 ered w r hile hot into water in order that the potassium chloride 

 may be leached out. It is claimed that in this way more than 80 

 per cent of the potassium of the feldspar may be extracted, and 

 that feldspar rock containing 10 per cent of potassium oxide may 

 be readily obtained on the large scale. The authors have made 

 careful estimates of the cost of this operation on a commercial 



Am. Jour. Sci.— Fourth Series, Vol. XXXIX, No. 231.— March, 1915. 

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