ON THE ASSAYING OF COALS BY THE BLOWPIPE. 219 



coal free from sulphur, with such proportions of iron pyrites as corres- 

 pond respectively to a per centage of 2, 4, 6, 8, and 10 parts of sul- 

 phur. These proportions are the following : Coal 96.26, pyrites 3.74= 

 sulphur 2 per cent. Coal 92.50, pyrites 7.50=sulphur 4 per cent. 

 Coal 88.76, pyrites 11.24=sulphur 6 per cent. Coal 85, pyrites 15= 

 sulphur 8 per cent. Coal 81.27, pyrites I8.73=sulphur 10 per cent. 

 Separate portions of each of these mixtures are to be fused in a plati- 

 num spoon with three parts of a mixture of five parts of carbonate of 

 soda with one part of borax (mixed beforehand, and kept for these 

 experiments in a receptacle of its own) ; and the fused mass is then to 

 be dissolved out in^ measured quantity of water. A single drop of 

 the solution is afterwards to be placed on a piece of silver foil (formed 

 for example by beating out a small coin), and suffered to remain upon 

 it for thirty seconds. The silver, wdped dry, is finally to be marked 

 on the back with the per centage of sulphur — 2, 4, &c. — contained in 

 the prepared coal. "When employing this method for the estimation 

 of sulphur, the coal under examination is to be treated in an exactly 

 similar manner, and the stain produced by it on a piece of clean foil, 

 compared with the test-stains on the separate silver plates. 



Finally, when the iron pyrites in the coal is not in a state of semi- 

 decomposition, the amount of pyrites, and consequently the amount of 

 sulphur, may be arrived at far more nearly than might at first thought 

 be supposed, by the simple process of washing in the agate mortar. 

 Each single part of pyrites, it will be remembered, corresponds to 0.53 

 of sulphur. A large piece of the assay-coal should be taken, and 

 broken up into powder ; and a couple of trials should be made on 

 separate portions of this. About 500 milligrammes may be taken for 

 each trial, and washed in three or four portions. In the hands of one 

 accustomed to the use of the mortar in reducing experiments, the re- 

 sults, owing to the lightness of the coal particles, and the consequent 

 ease with which they are floated off, come out surprisingly near to the 

 truth. In travelling, we may dispense with the washing bottle, by 

 employing, in its place, a piece of straight tubing drawn out abruptly 

 to a point. This is to be filled by suction, and the water expelled with 

 the necessary force by blowing down the tube. A tube six inches long 

 and the fourth of an inch in diameter will hold more than a sufficient 

 quantity of water to be used between the separate grindings. The 

 mortar should be very slightly inclined, and the stream of water must 

 not be too strong, otherwise, and especially if the coal be ground up 

 too fine, portions of the iron pyrites may be lost. The proper manipu- 

 lation, however, is easily acquired by a little practice. 



