144 



The so-called weatheriug of coal he ascribes to the absorption of oxy- 

 gen, which in one case oxidijies a portion of the carbon and hydrogen 

 of the coal, converting it into carbonic acid and water; in the other, 

 entering directly into the composition of the coal. If then the coal 

 becomes heateil in any way, a more or less energetic chemical action, 

 varying in proportion to the elevation of the temperature, takes place 

 upon the combustible substance of the coal ; but on the other hand 

 the process of oxidation jiroceeds so slowly that the changes occurring 

 within the period of a year can scarcely be established with certainty, 

 either technically or analytically. 



Moisture, as such, seems to have no accelerating influence upon the 

 weathering of the coal, the positive effect being generally appreciable 

 in coal (.'ontaining a large amount of sulphuret of iron or pyrites, the 

 decomposition of which is accelerated by the water. 



Another proposition of our author is, that i)ure coal, heaped up for 

 nine months or a year, unprotected from the weather and not allowed 

 to becoii.e heated, is changed no more than it would have been in a per- 

 fectly dry locality. As long as any increase of temperature does not 

 exceed certain bounds, as from 34:0'^ F. to 375°, there is no appreciable 

 loss of weight by the weathering ; and, in fact, there should be a slight 

 increase in consequence of the absorption of oxygen. The decrease in 

 value for combustible purposes, and for other technical applications, 

 which coal experiences by the weathering, is produced by a slight de- 

 crease of carbon and hydrogen, and an absolute increase of oxygen in 

 consequence of the exi)osure. 



Injury to vegetation from gas. — It is by no means an uncom- 

 mon assumption that illuminating gas, in escaping from pipes into 

 the soil, exercises a poisonous influence upon vegetation ; and a suit 

 was recently brouglit at Aix-la-Chapelle, by the city authorities, 

 against a gas company for recovery of supposed damage to the shade 

 trees of the city, resulting from their careless method of laying the 

 pipes. This was the cause of a detailed series of experiments in re- 

 gard to the assumed fact, and somewhat to the surprise of every one it 

 was asceitaine<l that puritied illuminating gas had really little or no 

 injurious effect of the kind asserted. The experiments were conducted 

 by eminent chemists, and included trials with pure hydrogen, light car- 

 buretted hydrogen, and heavy carburetted hydrogen, as well as puritied 

 illuminating gas. A discharge, during an entire day, of these various 

 gaseous substances into the soil of vessels containing growing plants 

 was found to produce little, if any, hurtful result. It was ditferent, how- 

 ever, when these same gases were impregnated with the constituents 

 of coal tar, especially with carbolic acid, in which case, after a few days, 

 <i very decided injury to the vegetation was found to have taken i)lace. 

 Tlie effect seemed to be that these impurities, coming in contact with 

 the roots of the plants, deposit tarry matter upon them which ultimately 

 caused death by a kind of as[)hyxia. The smallest quantity of carbolic 

 acid was found to have a very decided influence; so that the principal 

 <jaution to be observed, as far as injurious results are concerned, is to 

 *ee that the carbolic acid is entirely eliminated. In one experiment a 

 <lischarge of gas was allowed to take place for three hours daily, for a 

 period of an entire year, and the effect, if anything, was to secure a. 

 fuller development of the phmt. 



All that those experiments ai)pear to prove, however, is that perfectly 

 l)ure illuminating gas is not injurious to the roots of vegetation, the 

 fact remaining demonstrable that ordinary gas does have a marked 

 noxious effect. The elaborate communication in lS,"i'S to the Philadel- 



I 



