TRANSACTIONS OF THE SECTIONS. 37 
value should, of course, be equal to the former; and without detaining the Section 
with the actual numbers which I have obtained, I may state that the method just ex- 
plained has completely established the accuracy of the expression which gives the 
force of vapour at the dew-point in terms of the difference of temperatures of the wet 
and dry thermometer, of the pressure of the air, and of the tension of vapour at the 
, temperature indicated by the instrument, whose bulb is kept moist, 
i “ I have only in conclusion to state, that the quantity w is got by slowly passing, by 
means of an aspirator, a known volume of atmospheric air through a system of two 
’ tubes, one of which is packed with small fragments of chloride of calcium, and the 
___ other with asbestos moistened by oil of vitriol.” 
¢ 
Some Remarks on the Chemistry of the Arsenites. By J. Apsoun, MD. 
This paper contained an account of a variety of experiments, made with the view 
_ __ of obtaining a more exact knowledge of the arsenites than can be acquired from 
books, +The substances chiefly experimented on were arsenite of copper, arsenite of 
lime, and arsenite of silver. 
_ Abstract of a Letter from Dr. Will of Giessen, on an Improved Method of 
ascertaining the commercial Value of Alkalies or carbonated Alkalies, Acids, 
& and Oxides of Manganese. 
& The apparatus by which this determination is effected consists of two small glass 
flasks (A and B), connected by the bent tube c, which passes through corks in the 

_necks of the flasks. Into the flask A is put the solution of the substance to be tried, 
and into B is put concentrated sulphuric acid. Two other tubes pass through the 
_ corks in the flasks—the one, passing through the cork of A, dips below the surface 
_of the solution, and is closed with a small piece of wax, while the one in B is left 
_ open, and does not reach below the fluid contained in it. Suppose the flask A to 
contain a weighed quantity of a solution of a carbonate, then a known quantity of 
_ sulphuric acid is introduced into B, and the whole apparatus weighed: the tube 6 
_ being then closed with wax, if air be blown into a, a portion of the sulphuric acid 
passes over through the tube c into the flask A, and comes in contact with the car- 
bonate. The consequence is an evolution of carbonic acid, which must go through 
the concentrated sulphuric acid, and is thus made perfectly dry. When all the car- 
© 
_ 
oe he 
yo G 
_ 
3 
ma writ ry 
__ bonate is decomposed, the piece of wax on the tube d is removed, and air sucked 
___ through the tube a, in order to remove all the carbonic acid. The apparatus is then 
___ to be weighed, and, from these data, the quantity of alkali combined with carbonic 
___ acid may be easily calculated. The same method is applicable to the acids, particu- 


__. larly to vinegar, which was till now a very tedious and, at the same time, a very in- 
accurate operation. Dr. Will considers that the value of soda or potash can be thus 
___ determined with much greater accuracy than according to the method of Descroizell, 
improved by Gay-Lussac. If a soda contains a sulphite or a hyposulphite, which is 
a almost always the case, the alkalimetrical method in use at present gives quite wrong 
__ results: the same is the case if potash contains phosphates, silicates, &c, 



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y. 
