242 § 123. ANALYSIS OF ASHES. 



into an aiDpropriate furnace in such a manner as to be 

 heated mostly at the sides and on the top. The heat 

 must, at first, be kept very low for several hours, or even 

 days, while the substance is slowly charred ; the coal, 

 when so slowly formed, takes a more porous consistency. 

 When the evolution of gases has nearly ceased, the heat 

 may be gradually raised, but not at any time to a percep- 

 tible red ; in this way, at least in the incineration of most 

 of the fodder-plants, roots, and woods, that yield an ash 

 rich in carbonates, a perfect combustion is obtained with- 

 out fusing the ash. In case some coal remains, that re- 

 sists combustion without applying too high a heat, exhaust 

 it with hot water two or three times ; the washed residue 

 is usually very easily burned. Then either add the aque- 

 ous solution just obtained to the ash, evaporate the mix- 

 ture to dryness on the water-bath, ignite the residue very 

 gently, and weigh it ; or weigh the last ash, and bring 

 the aqueous extract of the coal to a certain volume, and 

 for each part of the subsequent analysis, mix together 

 equal fractional parts of ash and extract. 



Substances rich in silica, as the grasses, and the stems 

 and chaff of cereals, and also seeds rich in alkaline phos- 

 phates, are with difficulty made to yield an ash that is free 

 from coal. Such substances should first be charred at a 

 very low temperature ; then, witliout disturbing the coal 

 in the dish, moisten it with a cold saturated solution of 

 baric hydrate, dry the moistened mass, and ignite it in the 

 muffle at a barely visible red heat ; the completion of the 

 incineration generally requires from 8 to 12 hours. Enough 

 baryta water must be added, by moistening and drying 

 the coal several times, so that the ash will contain about 

 half its weight of baryta. The addition of this substance 

 almost entirely prevents the escape of the chlorine, effects 

 a more speedy combustion of the coal, makes the silicates 

 decomposable by acids, and insures the presence of phos- 

 phoric acid in the ash in a readily determinable form. 



