476 



J)t. M. C. Stopes. On the Four Visible 



the four constituents, so that only two" relevant chemical treatments will he 

 noted here. 



(i.) With 10 pe7' cent. KOH in Water -\- twice the Volume of 50' per cent. 

 Alcohol the behaviou.r of vitraiu is interesting. Small pieces (about 

 3x5 or 4x6 mm.) of pure vitrain placed in this solution, withovit any 

 previous treatment, and left in the cold, become slightly swollen and 

 softened without the addition of any acid or any other chemical substance. 

 In three or fo\ir days pieces in this solution acquire the consistency of hard 

 cheese or soap, and with an ordinary razor thin flakes can be cut from them.* 

 The vitrain alone, however, is affected in this way. The clarain, largely 

 breaks down when touched after being in the solution, and is hard and 

 irregular to the razor's edge. The durain becomes so friable that any 

 attempt to cut it with the razor breaks it down to a hard, gritty powder. 



The penetrating power of alcohol should not be forgotten in considering 

 the behaviour of coal to weak caustic solutions in it : a solutioii in water 

 alone has not the same effect. 



(ii.) W%th strong Nitric Acid + a few Drops of Hydrofluoric Acid, followed 

 later on hy Neutralisation. 



Otherwise untreated samples of coal, of the three specified ingredients of 

 coal other than fusain, placed in the mixture of acids, all tend after some 

 days to break down to some extent, and the acid becomes tinged with brown. 

 If left in the cold the pieces do not entirely disintegrate, but remain as 

 smaller' pieces. If after a week or so the acid is poured off, the pieces 

 drained and then neutralised with strong potassium hydrate, they may still 

 retain their solid nature. If the black solid mass is now placed- -iat the 

 bottom of a relatively large vessel, and water added in quantity, a 'pro;^o'i-tion 

 of each goes into solution as follows: — ' ■ 



Vitrain goes completely into solution if care is taken to select quite- pure 

 samples of vitrain. With the rapid addition of water there is ait bncte formed 

 a quantity of frothy " head," which ultimately, but very slowly, settles doWn. 

 The " solution " looks quite black in bulk, but when it fills a thin tube and is 

 held against the light, it is seen to be a clear tea-coloured liquid, containing 

 no floating particles or suspended jelly-like precipitate. Exact fiaeasurements- 

 of quantities are not yet significant, but I found that 2 grm. of pure 

 selected vitrain yield, with the addition of the necessary water, half a litre or 



* As a similar behaviour has been described for the ruu-of-mine Lignites, it should 

 be remembered that the coals dealt -with in the present paper are typical hard, true 

 black, bituminous, palseozoic coals ; and that one of the standard criteria of distinction 

 between lignite and true black coals is the fact that aqueous solutions of potassium 

 hydrate dissolve the former to some extent, with a brown solution, but do not affect the 

 latter. 



