CHEMICAL SCIENCE. 203 



arsenic (14 + Gl = 7-3); and the same to that of fluorine, gives that of bromine 

 (10 + 01=80). 



In a word, if the numbers be arranged on two parallel lines, the ordinates 

 of one scries lengthened by five, become the ordinates of the other, with the 

 single exception of phosphorus and chlorine, which are separated by 4'5 

 instead of 5. These facts teach the propriety of arranging the metals in 

 series, that shall show a double parallelism; for such a classification brings 

 out to view the various analogies existing among them. In fact, when 

 arranged by natural families, each of the elements is in proximity to two 

 others, belonging to two related families ; and these related families occupy 

 the two lines next to that containing the metal selected for comparison. 

 Finally, each metal is surrounded in such a table by four others, which arc 

 united to it by analogies of different kinds and more or less close. Corre- 

 spondence of Silliman's Journal. 



From a report of Dumas' paper in the Comptes Rendus, the following 

 additional details arc derived. 



In order to exhibit the numerical relations between the equivalents of the 

 different elements, the author, after referring to the previous investigations 

 of Professsor Cooke, takes up, in the first place, the examination of certain 

 groups and series presented by organic chemistry. If we consider the homolo- 

 gous series C2II.3, CJIs, CeHz, etc., we remark at once that there is a common 

 point of departure for and a common difference between the equivalents of 

 the successive terms. The formula a-\-nd represents the generation of all 

 these radicals, a being the equivalent of the first, and d the difference be- 

 tween the first and second term. The author remarks, that if we did not 

 know the law of progression, we might easily be led to think that the ratio 

 between the numbers 141 and 281, 127 and 2-53, 113 and 225, is the simple 

 ratio of 1 : 2, especially as chemistry can hardly decide with absolute cer- 

 tainty whether an element has, for example, the equivalent 225 or 226. The 

 formula deduced from the simple progression above mentioned would not 

 account for the generation of the elements, as Professor Cooke supposed. 

 But the organic radicals are not always produced by addition, but sometimes 

 by substitution, as we see in the compound ammoniums. We may have, for 

 instance, the following ammoniums : 



a-\-d 

 a-\-d' 



where a represents ammonia XH-i, and d, d f , etc. represent the equivalent of 

 hydrocarbons of the series C n H". 



In the next place, there arc certain radicals in organic chemistry where the 

 fundamental molecule itself changes, as well as the bodies added to or sub- 

 stituted in it. Thus, tin and ethyl form six molecular groups, possessing all 

 the properties of organic radicals. If we represent tin by .a, and ethyl by d' y 

 we have for the six species of stannethyl the formulas 



a + d' 



(nn-\-nd f ) being the general formula. With these premises the author pro- 

 ceeds to compare the equivalents of the elements. The elements F, C!, !;-, 



