406 MINERAL CONSTITUENTS OF THE ANIMAL BODY. 



bases ; and although this necessary change has not been over- 

 looked, the consequences have too often been neglected. When 

 in the first place we direct our attention to the sulphuric acid, we 

 shall find that the number representing this acid as found in the 

 ash, can scarcely ever correctly express the quantity of sulphuric 

 acid existing preformed in the organic substance, or the sulphur 

 contained in it. For if we suppose all the sulphur converted by 

 combustion into sulphuric acid, and united to the bases that had 

 previously been combined with organic substances or with carbonic 

 acid, a great portion of the sulphur must be lost, even when these 

 bases are sufficient for the saturation of the sulphuric acid that is 

 formed (which is not always the case, as, for instance, in the bile) 

 in consequence of the sulphates in contact with the nitrogenous 

 charcoal, which is so difficult of incineration, being converted into 

 metallic sulphides, of which a larger or smaller quantity will escape 

 as sulphurous acid during the prolonged process of calcination. 

 Under the action of a strong glowing heat common phosphate of soda 

 removes a part of the base, not only from the carbonates, (see p. 97,) 

 but also from sulphates of the alkalies, as well as from the metallic 

 chlorides of the ash, so that not only does all the alkaline carbonate 

 disappear from the ash, but a portion of the hydrochloric or sul- 

 phuric acid may be also lost. Where the ash contains acid phos- 

 phate of soda, as occasionally happens in urine devoid of lactic 

 acid, a portion of the phosphoric acid must necessarily be lost; for 

 we know with what difficulty carbon burns in the presence of 

 fusible salts, and it must be recollected that a portion of the phos- 

 phoric acid of the acid salts will be reduced by the carbon and 

 volatilised. These few remarks may suffice to show how little 

 atttention was formerly directed to the reciprocal decompositions 

 experienced by the mineral salts that occur in vegetable or animal 

 substances, under the influence partly of a simple glowing heat, 

 partly of heat in the presence of unconsumed carbon, and partly 

 of a glowing heat in oxygen gas. 



I have endeavoured in some degree to evade these obstacles in 

 the way of the determination of the mineral constituents of animal 

 bodies, by isolating organic substances as much as possible, 

 according to their solubility (as I have done in the case of blood,* 

 for instance,) and then determining the constituents of the ash of 

 each separate extract ; by which means we may be justified in 

 expecting that the soluble salts that are preformed in the blood 

 will be contained in the aqueous and alcoholic extracts, and that 

 * Berichte der k. sachs. Gesellsch. d. Wiss. Bd. 1, S. 98. 



