192 ' ANNUAL OF SCIENTIFIC DISCOVERT. 



Tliere are a groat many opinions afloat relative to the cause of 

 spontaneous crtnibustion, some ascribing it to tlie eliemical com- 

 position of tlio coal, others to the absence of ventihition, either 

 natural or artificial, while others, again, consider it is caused by 

 moisture. 



1. As to the chemical composition of coal. Owners know that 

 one kind of coal is more liable to lieat than another, and some 

 will not .<hip tliat which is dangerous; but others are less scrupu- 

 lous, and ship all kinds. This might be partially cheeked by 

 obliging owners to deposit at the Customs an analysis of the coals 

 sent by them; tliey would be afraid of having any lire traced to 

 their coal. lUit a better method is suggested by ]\Ir. R. Hunt, 

 F.lt.S., of the Museum of Practical Geology, in England. A ma- 

 chine has for some time been employed for washing away the iron 

 pyrites, or bisulphuret of iron, from the small coal at the pit's 

 mouth, previous to converting it into coke. AV'hih? the coal is in 

 transit, the oxygen acts upon the bisulphuret of iron, and evolves 

 great heat; consequently, if the iron p3rites were excluded, a 

 great source of danger would l)e obviated. The cost is only about 

 sixpence a ton for the washing, and would Ije amply set olf by 

 the lower rate of insurance consequent on greater security. 



2. As to natui'al ventilation. It is chiefly small coal which 

 heats; there l)eing room in large kinds for the air to circulate be- 

 tween the lumps; but as the Chilian consumer requires small 

 coal for smelting purposes, the only remedy is for shippers to send 

 as large coal as can he used. 



3. Artificial ventilation. Mr. Hunt proposes a method of se- 

 curing this; but its ellicacy has not yet been prov(!d. It is to let 

 down a pijje in the after part of the ship well into the coal, and to 

 let down one in the fore part, with the top communicating with 

 the eh.imney of the cook's galley; this would produce an up 

 draught, and keej) down the temperature of the coal. 



4. Aloisture. Coals are in every way liable to get wet. At the 

 pit's mouth they lie uncovered ; in the wagons they are not in any 

 way protected, the expense of tarpaulins ba'ing too great. While 

 being shipi)ed, the hold is open to the weather; and at sea the 

 hatches are frequently taken off, and the spray and sea air must 

 neeessai'ily dampen them. 



On the whole, the committee commended to those connected 

 witii shipping coal — 



That coal of undue fineness or damp coal should not be shipped. 



That a rod similar to those used in British ships should be used 

 every twelve or twentj'-four hours, to ascertain the temperature 

 of the coal. 



That the proposition of Mr. Hunt for artificial ventilation should 

 be tried. 



That the coal should be washed previous to shipping. — Scien- 

 tific American. 



PROTECTION OF VESSELS' HULLS. 



The Jouvin composition for protecting the hulls of ships has 

 been tried on the French armor-plated vessel, the "Helene," which 



