N AND THE IIVDIJOCAKIJONS 333 



of coal were formed, 6 which, following the example set by England, are 

 now utilised everywhere as the principal material for heating steam 



uncl lastly a colourless acid also soluble in water (crenic acid). Alkali dissolves a part 

 of the original brown and black substances, forming solutions of a brown tint (ulmic 

 and humic ai-idsi, which sometimes communicate their colour to springs and rivers. The 

 composition of the humus in the soil is generally in connection with its fertility; firstly, 

 because putrefying plants develop carbonic anhydride and ammonia, and yield the saline 

 substances which are necessary to vegetation; secondly, because humus is capable of 

 attracting the moisture of the air and of absorbing water (twice its weight) and in 

 this way keeps the soil in a damp condition, which is indispensable for nourishment ; 

 thirdly, humus renders the soil porous, and, fourthly, renders it more capable of absorb- 

 ing the heat of the sun's rays. On this account black earth is often most remarkable for 

 its fertility. One object of manuring is to increase the quantity of humus in the soil, 

 and any easily changeable vegetable or any animal matter (composts) may be used. The 

 boundless tracts of black earth soil in Eussia are capable of bestowing countless wealth 

 on the country. 



The origin and extent of black earth soil is treated in detail in Professor Dokou- 

 ^haeff's works. 



If those substances which produce humus undergo decomposition under water, less 

 carbonic anhydride is formed, a quantity of marsh gas. CH 4 , is evolved, and the 

 solid residue forms an acid humus, found in great quantities in marshy places, and 

 called peat. Peat especially abounds in the lowlands of Holland, North Germany, 

 Ireland, and Bavaria. In Russia it is likewise found in large quantities, especially in the 

 North-west districts. The old hard forms of peat resemble in composition and properties 

 brown coal ; the newest formations, as yet unhardened by pressure, form very porous 

 masses which retain traces of the vegetable matter from which they have been formed. 

 Dried (and sometimes pressed) peat is used as fuel. The composition of peat varies 

 considerably with the locality in which it is found. When dried in air it does not contain 

 less than 15 p.c. of water and 8 p.c. of ash ; the remainder consists of 45 p.c. of carbon, 

 4 p.c. of hydrogen, 1 p.c. of nitrogen, and 28 p.c. of oxygen. Its heating power is about 

 equivalent to that of wood. The brown earthy varieties of coal were probably formed 

 from peat. In other cases they have a marked woody structure, and are then known as 

 lignites. The composition of the brown sorts of coal resembles in a marked degree that 

 of peat namely, in a dried state brown coal contains on an average 60 p.c. of carbon, 5 

 p.c. of hydrogen, 26 p.c. of oxygen and nitrogen, and 9 p.c. of ash. In Russia brown coal is 

 met with in many districts near Moscow, in the governments of Toula and Tver and the 

 neighbourhood ; it is very generally used as fuel, particularly when found in thick 

 -Muis. The brown coals generally burn with a flame like wood and peat, and are 

 iikin to them in heating power, which is two or three times less than that of the best 

 coal. 



6 Grass and wood, the vegetation of primaeval seas and similar refuse of all geological 

 periods, must have been, in many cases, subjected to the same changes they now 

 undergo that is, under water they formed peat and lignites. Such substances, pre- 

 served for a long time underground, subjected to the action of water, compressed 

 by the new strata formed above them, transformed by the separation of their 

 more volatile component parts (peat and lignites, even in a finished state, still 

 continue to evolve nitrogen, carbonic anhydride, and marsh gases), form coal. Coal is a 

 dense homogeneous mass, dark brown or black, with an oily or glassy lustre, or, more 

 rarely, dull, without any evident vegetable structure ; this distinguishes it in appearance 

 from the majority of lignites. The density of coal (not counting the admixture of 

 pyrites, &c.) varies from 1'25 (dry bituminous coal) to 1'6 (anthracite, flameless), and 

 CM u reaches 1'9 in the very dense variety of coal found in the Olonetzky government 

 (termed thungite), which, according to the investigations of Professor Inostrantzeff, may 

 be regarded as the extreme member of the various forms of coal. 



In order to explain the formation of coal from vegetable matter, Caigniard de la Tour 



