492 SCIENTIFIC RECORD FOR 1884. 



explanation. The author thinks that there are indications that the 

 color of coLQpouuds is a periodic function of their atomic weights. 

 This is best seen in the normal iodides. He proposes extending his re- 

 searches to the colors of organic bodies. {Benchte d. cliem. Ges., xvii, 

 2151.) 



The Periodic Lmc and the Occurrence of the Elements inNature, by Thomas 

 Carnelly. — The theory concerning the occurrence of the elements in 

 nature is based upon the periodic law, and comprises four points : 



(1) Elements which belong to the odd series (of the periodic classi- 

 fication) are as a rule readily brought into the free condition. On the 

 other hand, those elements belonging to the even series are only set 

 free with difficulty. Carbon, nitrogen, oxygen, sodium, magnesium, 

 and silicon are the only exceptions to this rule, which is ex])lained by 

 the inverted character of the " curve of the elements." 



(2) Elements belonging to the even series, with the exception of 

 carbon, nitrogen, and oxygen, and the group VIII, never occur in nature 

 in a free state. The elements belonging to the odd series frequently 

 occur in this condition. 



(3) The elements belonging to the odd series occur in nature ordinarily 

 as sulphides or double sulphides (selenides, arsenides, &c.), i. <?., in com- 

 bination with a negative element belonging to an odd series, rarely as 

 oxides. Elements belonging to the even series are commonly found as 

 oxides or double oxides (with formation of silicates, carbonates, sulphates, 

 alumiuates, &c.), that is to say, in combination with a negative element 

 belonging to an even series, and never (with two exceptions) as sul- 

 phides. 



(4) The halogens chlorine, bromine, iodine, fluorine, the most electro- 

 negative elements, occur in nature in combination with the most electro- 

 positive metals, as chlorides, bromides, iodides, and fluorides, and (omit- 

 ting certain metallic oxychlorides and sulphochlorides) in combination 

 with oxygen or sulphur. 



The above-mentioned 'facts may be thus expressed with reference to 

 Lothar Meyer's curve of the elements : Elements whose ])lace is on fall- 

 ing parts of the curve are difficult to reduce, and never occur in nature 

 in a free condition or in combination as sulphides, but always in com- 

 bination with oxygen as oxides or double oxides (silicates, sulphates, 

 carbonates, &c.) ; while the elements whose place is on ascending parts 

 of the curve are easily reduced, and occur almost always — more or 

 less — in a free condition, and also in combination with sulphur and very 

 .rarely with oxygen. [Berichte d. chem. Ges., xvii, 2287.) 



Explanation of Gladstone and Tribe''s 2-3 Law in Chemical Dynamics, 

 by John W. Langley. — Gladstone and Tribe showed that if a plate of 

 metal is suspended in a solution of another metal which it can precipi- 

 tate, the rate of chemical action, as shown by the loss of weight in the 

 suspended jjlate (for a given period of immersion), will vary with the 



