THE FARMER AT HOME. 41 



rapid flame. Natural historians have divided them into several 

 genera ; but modern chemists arrange them according to their chem- 

 ical properties, and are only acquainted with six species, which are 

 very distinct from each other : these are, amber, asphaltos, jet, pit 

 coal, ambergris, and petroleum. 



BLACK. Something opaque and porous, that imbibes the great- 

 est part of the light that falls on it, reflects little or none, and there- 

 fore exhibits no color. Bodies of a black color are found more inflam- 

 mable, because the rays of light falling on them are not reflected out- 

 wards, but enter the body and are often reflected and refracted within 

 it, till they are stifled and lost. Black substances are generally found 

 to be lighter than white, being more porous ; clothes dyed of this color 

 wear out faster than those of any other, from the quantity of vitriol 

 necessary to strike the dye. 



BLAST. A disease of plants, to which by different writers has 

 been given the name of blight, blast, and mildew. The latter, how- 

 ever, is evidently a distinct disease, and produced by different causes. 

 Blast or blight has been divided into several varieties, affecting plants 

 in different ways, and with varying intensity. Among these may be 

 mentioned blight originating from cold. The north or easterly winds 

 of spring often produce this, by freezing the tender shoots, or by re- 

 tarding the flow of the juices. Thus the young fruits are deprived of 

 their nourishment, and fall from the stem. Blast or blight from sultry 

 wet weather, originating contagious diseases of plants, is another of 

 the forms noted, and mildew sometimes seems to result from this 

 cause. 



The blight which sometimes strikes the grain of whole districts, 

 v/ould seem to be owing to atmospheric causes thus generated, since 

 the disease appears to follow, and be governed by the course of winds. 

 Blast from the want of nourishment, is another form, but of which the 

 cause is usually obvious. Impoverished land, too great quantities of 

 seed, or injudicious culture, may produce this blight; but in this coun- 

 try, it is oftener observed as the effect of drought. Blast from fungi 

 is the kind of blight which attacks grain also, and which has been 

 erroneously attributed to particular plants, as the barberry bush, since 

 the fungi on the leaves of this plant, and those that cause the blight 

 in wheat, are clearly distinct. 



BLASTING OF ROCKS. The process of blasting rocks, or stones, 

 consists in boring a cylindrical hole, about ten or twelve inches deep, 

 in the rock, by means of a chisel for that purpose. The lower part 

 of this hole is filled with gunpowder. The upper part of the hole is 

 then filled up with fragments of stone, firmly rammed together ; a 

 hole being left through these materials, by the insertion of an iron 

 rod, which is turned round during the operation of ramming. This 

 hole is next filled with powdar, and a match is applied to it in such 

 a manner, that the operator has tim* to run out of the reach of the 



