340 Dr. Macnevoi's Exposition of [Nov. 



3, three atoms. The27'6is, therefore, a deutoxide, viz. 1 atom 

 metal + 2 atoms oxygen, and the 41 a tritoxide of 1 atom metal 

 + 3 atoms oxygen. Hence, these proportions are as 



Here, the weight of the atom of nickel comes out nearly iden- 

 tical. The mean of 7-305 + 7-317 h- 2 = 7-311 weight of the 

 atom of nickel. But others consider the compound 100 metal 

 4- 28-74 oxygen a protoxide ; in that case the atom of nickel 

 would be only half the weight assigned to it. Dr. Thomson says 

 3-375, and thinks 100 metal + 29-63 the proper proportions. 



70. CohaU. — There are two known oxides of cobalt, the blue 

 and the black. From the analysis of RothofF they appear to be 

 composed of 100 metal + 27-3 oxygen and 100 metal + 40-95 

 oxygen. Now, these are to each other as 2 to 3, and the weight 

 of the atom of cobalt may be had like that of nickel. It is 7-326. 



It is to be observed of cobalt in like manner as of nickel, that 

 its atom will either be 7*326 or half that number, according as 

 we make 100 metal + 27*3 a protoxide, or a deutoxide. Dr. 

 Thomson supposes the peroxide composed of two atoms metal 

 + three atoms oxygen, which would give the number 3-625 ; but 

 I think the supposition is inadmissible, because it resolves itself 

 into 1 atom metal + 1'5 atom oxygen. 



It will be seen that oxygen unites with nickel and cobalt 

 nearly in the same quantity, and that the weight of the atoms of 

 these metals is almost exactly the same. Generally, if not inva- 

 riably, it will be found that the weights of atoms are to each 

 other iiiverseii/ as the quantity of oxygen with which equal 

 quantities of each metal combines to form similar oxides. Thus, 

 13-71 weight of an atom of silver is to 25 weight of an atom 

 of mercury as 3-99 oxygen in the protoxide of mercury to 7-272 

 oxygen in the protoxide of silver. The same will apply to the 

 other states, as they are all multiples of the protoxides; whence 

 we may infer that where the weight of oxygen is the same in 

 any similar oxides, the weight of the atoms will be the same. 

 The oxides and atoms of nickel and cobalt, considered in either 

 Vt'ay, are illustrations in point. 



71. Manganese. — According to Dr. John, sulphate of manga- 

 nese contains 100 parts acid combined with 92*06 parts protoxide 

 of mauQ-anese. Hence, from what has been said before concern- 

 ing the oxygen of acids and bases combined, 92*06 parts 

 protoxide of manganese contain 20 parts oxygen, and being 

 composed of I atom oxygen + 1 atom manganese, we have the 

 following proportions to determine the weight of the atom, as 20 

 oxygen : (92*03 — 20) 72*06 manganese :: 1 atom of oxygen : 

 3-6'03 atom of manganese. From other considerations, Dr. 

 Thomson considers 3-500 more near the truth. 





