2o8 SO.ME NOTES ON TREATMENT OK SANDS FOR STOPE FILLING. 



the cyanide present, the first stage in the reaction being- forma- 

 tion of potassium cyanate, which afterwards breaks up into car- 

 bon dioxide, ammonia and nitrogen ; (2) that only shght excess 

 of permanganate is required ; (3) that the cost for permanganate 

 works out at between 6d. and gd. per ton of sands. The reac- 

 tion evidently takes about four hours to complete. At the July 

 meeting of the same Society Mr. White gave some results of 

 experiments with bleaching powder as a "cyanicide. " He stated 

 that, as with permanganate, in alkaline solution potassium cyanate 

 is formed, and this afterwards breaks up, forming ammonia, 

 nitrogen and carbonate of potash. Mr. White explained that 

 unless alkaline solutions are used there is a danger of cyanogen 

 chloride being formed, a body which is nearly as poisonous as 

 cyanide itself. The advantage of bleaching powder over per- 

 manganate is greater cheapness. It is interesting to note that 

 both permanganate and bleaching powder have been used, on the 

 large scale, in conjunction with the method of sand filling referred 

 to as described by Mr. Powell, and both are said to have given 

 satisfactory results. 



The writer has been concerned in the making of some experi- 

 ments to find out the action of a solution of polysulphides of 

 calcium on cyanide in current sands. This solution is prepared 

 by boiling sulphur and slaked lime together in water. Small 

 scale experiments indicate that, given time, comparatively slight 

 excess of this body in presence of alkali can completely convert 

 the cyanide into the harmless and stable sulphocyanide, and with 

 considerable excess of the polysulphides the cyanide can be com- 

 pletely converted in about five minutes. The experiments were 

 made with sands containing a relatively high percentage of 

 cyanide. The serious results which might arise from the presence 

 of prussic acid in the atmosphere of a mine have already been 

 referred to. There is little doubt, however, of a tendency in 

 certain quarters to exaggerate the danger, and it is quite pro- 

 bable that in decntly ventilated places a little prussic acid might 

 be allowed to pass into the atmosphere without risk. On this 

 question hangs the closely related one of whether it is necessary 

 to destroy all cyanide present in the sands before they enter the 

 mine, and if not, what percentage may be left in them. This is a 

 difficult question and one to which no student of the subject in 

 this country has risked a definite answer. Some experiments on 

 this point, carried out on right lines, would be of considerable 

 interest even if no very definite results were to be obtained. 



In conclusion, I beg to express the hope that these notes will 

 help to give an idea of what has been done in this country in 

 regard to this highly important but comparatively recent develop- 

 ment of the Mining Industry, and at the same time convey some 

 notion of the difficulties which have been, and have still to be 

 overcome. 



The papers which have been read on the subject and the 



discussions which have taken place at the meetings of the 



Chemical, Metallurgical and Mining Society, besides having 



a decided influence on the progress already made 



