M. ^s\iex on the Bichromate of Per chloride of Chrome. 83 



two meridian planes passing through the perpendicular to thai 

 front, or, in other words, the intersection of a plane drawn through 

 either ray belonging to a front perpendicular thereunto is always a 

 line of vibration in that front. 



This has been noticed, I think, by Sir William Hamilton for the 

 particular case of the singular points. 



As two fronts belong to every ray, so two rays pertain to every 

 front. And from what has been said above it appears that the two 

 lines of vibration in any front are the projections of its two rays 

 upon its own plane. 



XVI I. Notice on the Bichromate of the Per chloride of Chrome, 

 By M, Walter*. 



I HAVE constantly succeeded in the preparation of this com- 

 pound by employing the quantities and process following : 



I placed in a tubulated glass retort 100 parts of sea-salt 

 dissolved, and 168 parts of neutral chromate of potash, the 

 whole being well mixed and reduced to a very fine powder ; 

 I then fixed to the retort a tube and a receiver with two aper- 

 tures, and poured by degrees, through a tube in the form of an 

 S, which was fixed in the aperture of the retort, 300 parts of 

 concentrated sulphuric acid. 



The liquor thus obtained is of a beautiful blood-red colour ; 

 it is volatile, and sends forth vapour copiously ; when placed 

 in contact with a quantity of water, it falls to the bottom in 

 drops of an oily appearance, and changes into chlorhydric 

 acid and chromic acid ; its boiling point is fixed and takes place 

 at 118° Cent, under the pressure of 0"^'76 ; its specific gravity 

 at the temperature of 21° Cent, is 1*71 ; it attacks mercury 

 with great activity, for this reason all contact with this metal 

 must be avoided; it is decomposed by sulphur, detonates 

 with phosphorus, dissolves chlorine and iodine, and com- 

 bines with ammonia with a disengagement of light. A small 

 quantity mixed with concentrated alcohol combines with a vio- 

 lent explosion, and the inflamed alcohol is scattered with force. 

 This unexpected action very nearly deprived me of my sight, 

 and has burnt me in a most dreadful manner. 



The bichromate of the perchloride of chrome is composed 

 according to my analyses, of 



Chlorine ^S*!^ 



Chrome 35-58 



Oxygen 19*28 



This result agrees with that obtained by H. Rose, and with a 

 combination calculated according to the formula 2 Cr O^ + 

 Cr O^ 



♦ From the Comptes Rendus, No. 9% 2nd Ser. 1837- 

 M2 



