326 Dr. Thomson on [Not. 



but the prisms were not large enough to allow the measurement 

 of the angles of the terminal faces. The crystals are not altered 

 by exposure to the air. 



Its taste is cooling, bitter, and metallic, and it leaves a hot 

 impression in the mouth, which, however, does not last nearly 

 so long as the taste of the chromate of potash. 



It is much less soluble in water than the chromate. Fifty-five 

 grains of water, saturated with it at the temperature of 63°, left, 

 when evaporated to dryness, 5-2 grs. of bichromate. We see 

 from this that at the temperature of 63°, 100 grs. of water are 

 capable of dissolving 10'44 grs. of this salt. Chromate of pot- 

 ash is more than four times as soluble. Thus the bichromate of 

 potash agrees with bitartrate and binoxalate of potash in being 

 much less soluble than the corresponding salt composed of an 

 atom of acid and an atom of potash. 



The aqueous solution of bichromate of potash has an intense 

 orange colour, similar to chromate of lead. It reddens vegetable 

 blue colours. 



It is insoluble in alcohol. Its specific gravity is 1-9801. 



When 100 grs. of the dry crystals were kept for an hour at 

 the temperature of 400°, they sustained a loss of weight amount- 

 ing to six grains. When the salt thus dried was exposed to a 

 red heat, it melted into a transparent red liquid, which, on cool- 

 ing, concreted into a semitransparent red salt, without under- 

 going any additional loss of weight. 



The action of tliis salt upon the different reagents is almost 

 the same as that of the chromate, making allowance for its infe- 

 rior solubility in water. It is, therefore, unnecessary to enter 

 into particulars. 



I have given this salt the name of bichromate, because I have 

 ascertained by experiment that it is a compound of two atoms 

 of chromic acid with one atom of potash, while the chromate is 

 a compound of one atom acid -f- one atom potash. 



Take 19 grs. of bichromate previously exposed to a red heat, 

 dissolve them in water, and precipitate by nitrate of lead. The 

 chromate of lead obtained, after being washed, dried, and 

 exposed to a heat of 400°, Avill be found to weigh 41 grs. Now 

 .^of41 is obviously 13. It follows from this, that 19 grs. of 

 bichromate of potash contain 13 grs. of chromic acid. The 

 residue is potash. Hence the salt is composed of 



Chromic acid 13 or 68-421 



Potash 6 31-579 



19 100-000 



If the reader will look back to the table exhibiting the compo- 

 sition of chromate of potash, he will see that it is a compound 

 of 6-5 acid + 6 potash ; while the bichromate is a compound of 



