[ 33 ] 



VII. Notices nf the Results of the Labours of Continental 

 Chemists. By Messrs. W. Francis and H. Croft. 



[Continued from vol. xix. p. 452.] 



On Citric Acid. 



VyACKENRODER has attempted to show that there is 

 only one hydrate of citric acid, the formula of which is 

 C- H^*^ O'^ and which is the common acid, whose crystals 

 have been measured by Brooke. Marchand has made some 

 experiments on this subject ; he found that the common acid 

 of commerce contains 34'4'5 per cent, carbon, and 4*86 per 

 cent, hydrogen. This acid was then crystallized at a tem- 

 perature not exceeding 60° C. The crystals had the same 

 form as described by Brooke, and, after having been pressed 

 and dried between bibulous paper, were found to contain 34'72 

 per cent, carbon, and ^'69 hydrogen. The formula for this 

 acid is exactly C'^ H^^^ O'^. When dried in vacuo over sul- 

 phuric acid the crystals lose two atoms, or 8-5 per cent, of 

 water, which is exactly the quantity that it loses when heated, 

 according to Berzelius ; the acid so obtained agrees with 

 Wackenroder's formula, viz. C' H"^ O''*. 



If a concentrated solution of citric acid be evaporated at a 

 temperature of 100° C. until a crystalline pellicle is formed 

 on the surface and then allowed to cool, the first crop of cry- 

 stals consists of small, scarcely determinable individuals, which, 

 according to Gustav Rose, are quite different in form from 

 those described by Brooke. Afterwards the first compound 

 crystallizes out of the mother liquor. This hydrate has the 

 formula C'- H^^'O''*. Berzelius heated it with oxide of lead, 

 and found its formula to be C'^ H''^ 0% for it lost 14 per cent, 

 water; but it is evident that he had converted the acidC^ H'''' 

 O'* into C12 H^o O^K—Annalen der Chemie und Pharmacie, 

 vol. xxxviii. p. 346. 



On the Compounds of Bichloride of Tin 'with the Alkaline 

 Chlorides. 

 Dr. BoUey has examined these salts. The bichloride was 

 prepared by passing chlorine into a solution of the protochlo- 

 ride of tin. By mixing together dilute solutions of bichloride 

 of tin and sal-ammoniac and slowly evaporating, a salt is ob- 

 tained which crystallizes in small regular octahedrons, some- 

 times combined with the hexahedron. They are not chano-ed 

 by exposure to the aii-, and contain no water. Formula 

 Sn CI'* + W IV Cl% By boiling a dilute solution the whole 

 of the oxide of tin is precipitated : this fact explains its value 

 as a mordant ; it is known to the calico-printer under the name 

 Vhil. Mag. S. 3. Vol. 20. No. 128. Jan. 1842. D 



