REPORT ON CHEMISTRY. 
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lvW 
drogen and arsenic formerly known. This compound was also 
discovered by Rose, and is obtained in the form of a yellow in¬ 
soluble powder when phosphuret of potassium is dissolved in 
water. It is more difficultly fusible than phosphorus, and at 
the moment of melting gives off hydrogen and vapour of phos¬ 
phorus. To prepare the phosphuret, Magnus* recommends 
that the two elements should be heated together under naphtha, 
by which means the danger of breaking the tube, which exists 
when they are heated alone, is avoided. 
Phosphoric Acid. —The remarkable property possessed by 
phosphuretted hydrogen, of assuming two mutually convertible 
isomeric modifications, is possessed in a still more striking de¬ 
gree by phosphoric acid. It is several years since Engelhart 
and Berzelius remarked that phosphoric acid, prepared by 
burning phosphorus in oxygen gas, or by oxidizing it with 
nitric acid, and fusing at a high temperature, if dissolved imme¬ 
diately in w^ater, possessed the property of coagulating albu¬ 
men, which it again lost by remaining in solution a few days. 
Soon after, the attention of chemists was more particularly di¬ 
rected to this object by the discovery of Mr. Clarke,—that a 
similar change was produced on the common phosphate of soda, 
by heating to redness. In its usual state the solution of neutral 
phosphate of soda precipitates from nitrate of silver a yellow 
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precipitate, which is' a sesquiphosphate of silver (P + 3 Ag); 
after heating to redness it precipitates a white salt, which is a 
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neutral phosphate, P +2 Ag. A similar white salt Berzelius 
found to be thrown down by the heated acid,—an observation 
afterwards confirmed by Gay-Lussac, thus connecting the ap¬ 
pearances observed by Engelhart with those of Clarke’s heated 
phosphate. For the acid in this second state Mr, Clarke pro¬ 
posed the name^yrophosphoric acid. When the discovery of 
the identity of the tartaric and racemic acids rendered it de¬ 
sirable to have a general prefix to denote change of properties 
without change of composition, Berzelius proposed %c*.qoc for this 
purpose, as involving no theory, and merely marking out that an 
alteration had taken place. Thus the racemic is the paratar- 
taric ; the fulminic, the paracyanic ; &c. And as the first state of 
the phosphoric acid seems to be that in which it is obtained im¬ 
mediately on burning phosphorus in oxygen gas, from which, in 
a few days, it changes into the common phosphoric, he proposed 
to call the new acid the phosphoric, and the old acid the para- 
Poggendorf’s Annalen, xvii. p. 527. 
