444 Mr. Carrington on the Evidence of the 



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 a 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 suflfei'ed 

 to remain upon it for thirty seconds. The silver, wiped dry, is 

 finally to be marked on the back wdth 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 exa- 

 mination 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 sulphm-, 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 0o3 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 por- 

 tions 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 results, owing to the lightness of the coal particles, and the 

 consequent ease with which they are floated off, come out sur- 

 prisingly 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 6 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 manipulation, however, is easily acquired by a little practice. 



LV. On the Evidence which the Observed Motions of the Solar 

 Spots offer for the Existence of an Atmosphere surrounding the 

 Sun. By \\. C. Carrington, Esq*. 



THE protuberances observed around the sun's pei-iphery 

 during total solar eclipses, and the excess of light and heat 

 radiated from the centre of the disc as compared with the parts 



* From the Monthly Notices of the Royal Astronomical Society, April 9, 

 1858. 



