T. 8. Hunt on the Crystalline Limestones of N. America. 193 
4 
of aqua-regia composed of two parts of hydrochloric and one of 
nitric acid. The retort being gently heated, the gases from 
antimony formed. This operation finished, the tube is removed, 
the tubulure closed, and the receiver, partly filled with water. 
being attached, the acid liquid in the retort is gently distilled to 
one-half its volume. We then examine the water of the recipi- 
ent, and if any arsenic is present, it will be found in the dist 
tilled liquid; if this metal be absent, we find nothing in the 
water, or at most, some traces of antimony, in case the operation 
has not been well conducted. If the gas contained any antimony 
it will all be found in the retort, in the state of perchlorid. 
I have not deemed it necessary to present the numerical results, 
which in repeated experiments have shown the great accuracy of 
these methods, but believing that chemists will at once recognize 
the value of the proposed processes, it is sufficient for me to have 
called their attention to the following facts, in part already known, 
and in part new. 
Ist. ‘he power of hydrochloric acid to dissolve and decompose 
arseniuretted hydrogen. : 
- The solubility of metallic arsenic in the same acid, when 
concentrated. 
8d. The explanation of the reactions of arseniuretted hydrogen, 
With the perchlorids of gold and iron, and with the bichlorid of 
Platinum. 
th. The decomposition of arseninretted and antimoniuretted 
hydrogen by nitric acid, and by aqua-regia. ; ; 
_ 2th. Uhe application of these reactions to toxicological analy- 
Ss, for the detection and separation of arsenic and antimony. 
a 

Ant. XXIV. On some of the Crystalline Limestones of North 
AO ica ; by T. S. Hunz, of the Geological Commission of 
anada, 
o* Abstract of a paper read before the American Association for the Advancement 
of Science, at Washington, April, 1854.) 
Tre crystalline limestones of Canada, with those of New York 
the New England States, may be divided into four classes, 
belonging to as many different geological periods. The first and 
Mest ancient occur in that system of rocks, named by Mr. Logan 
the Laurentian series, which extending from Labrador to Lake 
Huron, forms the northern boundary of the Silurian system of 
Canada and the United States. ‘The lowest beds of the Silurian 
25 
Szuies, Vol. XVIII, No. 53—Sept., 1854. 
