CHEMISTRY 



By H. Carrington Bolton, 



Professor of Chemlstrij, TrinHij College, Hartford. 



GENERAL AND I'HYSICAL. 



The Color of Chemical Compounds (is a Function of the Atotnie Weights 

 of their Constituent Elcmcnts.^-Thomixs Carnelly liods tliat the color of 

 chemical compoumls depends on at least three conditions — (1) the tem- 

 perature, (2) tlie quantity of tlie electro-negative element, and (3) the 

 atomic weights of tbe constituent elements. Of these three conditions 

 the two former have been especially studied by Mr. Ackroyd, whose re- 

 sults are thuc, summarized: 



(1) All the chromium compounds change their color in a definite serial 

 order, that of the spectral colors, in such a manner that as the tempera- 

 ture rises the color approximates more and more to the red end of the 

 spectrum, and ultimately, at a sufldcieutly high temperature, passes into 

 brown and black. Most frequently the transition of color is direct from 

 white to a pale yellow, while violet, indigo, blue, and green are passed 

 over as transition stages. 



(2) In binary compounds an increase of the quantity of the electro- 

 negative element involves a change of color to the red end of the spec- 

 trnm, and ultimately into brown and black. 



(3) Dr. Carnelly expresses his law as follows. Influence of the atomic 

 weight: in some series of compounds. Ax Ry; Bx Ry; Cx Ry; &c., 

 in which R is an element or a group of elements, while A, B, C, «&;c., 

 signify elements belonging to the same subordinate group in Men- 

 delejeff's table of the natural classification of the elements, the color 

 passes entirely or partially through the following scale : White or 

 colorless, violet, indigo, blue, green, yellow, orange, red, brown, black, 

 with the increasing- atomic weight of the elements A, B, C, &c. In 

 other words, the higher the atomic weight of the elements A, B, C, rises, 

 the more the color of the compound approaches the red end of the 

 spectrum, and passes in certain cases into brown and black. This rule 

 applies only when the elements A, B, C, &c., belong to the same sub- 

 group. In 42G cases examined the author found only 14 exceptions, 4 

 four of which, DiClajVoO^, C1O3, and CdO, do not admit of satisfactory 



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