M. Bevzelius 07i Vayiadium. 7 



by dropping a perpendicular on the longer ; and by this con- 

 struction, we shall easily deduce the value of that diiference 



d^ = b m sin a ; 

 or, comparing this with the difference within the prism, we 

 have rf; = Did. 



These differences, therefore, are in the ratio of the refractive 

 powers; and the retarding effects exactly compensate each 

 other. 



The angle « should not be greater than 4° or 5°, if the 

 prism be ot glass. This experiment is very conveniently shown 

 by prisms of water or other liquid between glass plates kept 

 in the requisite position by small pieces of wax, which are 

 easily formed when other apparatus may not be at hand. 



II. 0)1 Vanadium. By M. Berzelius. 



[Concluded from vol. x. p. 337-] 



Perchloride of Vanadium. 



nPHIS is obtained by passing a current of chlorine gas over 

 -*■ suboxide of vanadium, mixed with a little dry charcoal. 

 The perchloride distils in the form of yellow drops, which 

 consist of a solution of chloride in the perchloride. This li- 

 quid is of a yellow colour; it is freed from the excess of chlo- 

 rine by passing a current of atmospheric air over it, previously 

 dried with fused chloride of calcium. When the air which 

 has passed over the perchloride no longer smells of chlorine 

 but merely of muriatic acid, the operation is to cease. In this 

 case a small portion of the perchloride is vaporized; in order 

 to avoid the slightest loss of vanadium, the air may be passed 

 into water, mixed with a little ammonia. After the separation of 

 the chlorine, the perchloride is of a much paler yellow. It does 

 not boil at 212° Fahrenheit; but it readily vaporizes by expo- 

 sure to the air, exhales a reddish yellow vapour, and deposits 

 vanadic acid in the state of an extremely fine powder. The 

 liquid part attracts moisture from the air, becomes red, after- 

 wards coagulates and deposits a subchloride. The liquid may 

 be diluted with water, which dissolves the coagulated portion ; 

 the solution has a pale yellow colour and a purely astringent 

 taste. When concentrated, this solution exhales chlorine, 

 becomes green when heated, and is eventually converted 

 chiefly into protochloride. Pure alcohol colours the perchlo- 

 ride red, and in a short time a small quantity of a'llier is 

 formed, while the liquid is at first green and afterwards blue. 

 Potassium may be preserved under the anhydrous perchlo- 

 ride ; 



