42 HOFFMANN ON HTGEOSCOPICITY 



periods of 93, 120, *70, 90, aud 48 hours, which resvilted iii an additional loss of respec- 

 tively 0-53, 0-53, 0-16, 0-lG, aud 005 per cent., or for the total period of 421 hours (addi- 

 tional to the preceding 354 hours) a combined loss of 1"43 per cent. In like manner a 

 lignitic coal which had previously been submitted to an exposure of 354 hours, was also 

 further exposed for consecutive periods of 93, 120, aud *70 hours, aud with the result that 

 it incurred an additional loss of respectively 0'34, 0"32, aud 008 per cent., or for the total 

 period of 283 hours (additional to the former 354 hours) an aggregate loss of 0-'74 

 per cent. 



The period of exposure— both in a dry and moist atmosphere — finally adopted, iu all 

 cases, was 354 hours, weighing at intervals of 190, 94, aud 70 hours ; aud it was found 

 that, during the last 70 hours of this exposure — 



In a dry atmosphere, the loss incurred by the — 



Lignites ranged from 0'3o to 0'58 per cent., the average loss being 0'42 per cent. 



Lignitic coals „ „ 0-13 to 0-26 „ „ „ „ 020 „ 



Coals „ „ 0-02to0'10 „ „ „ „ 0-05 



Semi-antliracites „ „ O'Ol to 0'02 „ 



Anthracite aniouuted to 005 per cent. 



In a moist atmosphere, the amount of water reabsorbed by the — 



Lignites ranged from 0'26 to 0'85 per cent,, the average gain being 0"55 per cent. 



Lignitic coals „ „ 0-07 to 0-26 „ „ „ „ 0-19 „ 



Coals „ „ 0'02to0-12 „ „ „ „ 0-07 



Semi-anthracites „ „ 0'02 to 0-04 „ „ „ „ 0-03 „ 



Anthracite amounted to 0"0l) per cent. 



The peat and authracitic coal comported themselves, in both above regards, iu much 

 the same manner as a lignite and coal respectively. 



It will be observed that there is a remarkably close agreement iu the amounts of 

 water lost aud reabsorbed by each of the respective A'arieties of fuel during the last 10 of 

 the 354 hours exposure, and that the amount of this loss aud reabsorption is (apart from 

 the anthracite) proportionate to the degree of alteration of the fuel — it being greatest in 

 the lignites, aud least in the semi-anthracites. 



From the above results, coupled with those obtained in the preliminary experiments, 

 it is evident that, beyond a certain point, the lignites and lignitic coals part with their 

 water but very slowly, so that even after an exposure of 354 hours to au absolutely dry 

 atmosphere, these yet retain a certain amount of water removable by a yet more protracted 

 exposure. The coals and semi-anthracites, on the other hand, may fairly be regarded as 

 dry after such period of exposure — indeed it was found that, iu many instauces, the semi- 

 anthracites aud more altered coals had, during the last 70 hours, suH'ered no alteration iu 

 weight. 



In the accompanying table the various fuels have been arranged iu the order of their 

 diminishing hygroscopicity. On referring to the same it will be seen that the capacity 

 for retaining, aud with it that for reabsorbing, water varies with the degree of alteration 

 which the fuel has undergone — it being most pronounced iu the lignites, less so in the 

 lignitic coals, aud least in the coals. Thtis, we find that the amount of water retained by 



