558 On the Cause of Clvcmkal Proportions. [Mat, 



sufficient to dissolve the whole, it has frequently hap^iened to me 

 that the whole black osidc was dissolved and a beautitul red oxide 

 left beliind. When I treated the mass with nitromutiatic acid, I 

 oxidated the black oxide, and then precipitated the whole with 

 caustic ammonia. The red oxide thus obtained being well washed 

 and dried, had gained an increase of weight by the oxygen absorbed 

 by the black oxide. But in all my experiments this increase was so 

 little that the black oxide must have been combined with a quantity 

 of red oxide 3, 5, or 6 times that of the black ; that is to say, that 

 these minerals contain much more peroxide than the oxide produced 

 by the vapour of water does. 



Several chemists are of opinion that there is a white oxide of 

 iron. I made the following experiment to verify this opinion. In 

 a phial I poured diluted muriatic acid on pure iron filings, and I 

 boiled them together till the acid was saturated. During this opera- 

 tion the phial was closed by a tube which conveyed the hydrogen 

 gas under water. I had placed a phial of caustic potash quite in 

 the neighbourhood of this mixture, and I had boiled it half an hour 

 to drive off the atmospheric air. When the muriatic acid was 

 saturated I decanted the muriate by means of a funnel which went 

 to the bottom of the alkaline ley, and continued pouring it in till 

 the phial was completely filled. I then stopped its mouth with a 

 tube, which passed into a small pneumatic apparatus. At the line 

 of contact of the two liquids in the phial a white precipitate 

 appeared, and when I mixed the liquids the whole became thick 

 and white. 1 then heated the w'hole till it boiled. The liquid 

 increasing in bulk made its escape through the tube, and^he white 

 matter at the bottom of the phial became black, and the same 

 change gradually took place in the whole precipitate, without the 

 disengagement of any gas whatever to prove that it had al)sorbed 

 oxygen during this change ; for in that case it would have decom- 

 posed water, and hydrogen of course would have been disengaged. 

 This experiment ])roves that the pretended white oxide is only the 

 hydrate of the black oxide, which, like the hydrates of tin and 

 copper, is decomposed at tlie temperature of boiling water. Hence 

 it follows that the protoxide of iron is a black matter, which some- 

 times owes its white colour to water, sometimes to carbonic acid, 

 as in sparry iron. 



I consider these experiments as proving that there is no probabi- 

 lity that there exists an intermediate oxide between the black and 

 red oxides of iron. 



26. Zbicmn, zinc (Zn), — I have found that 100 parts of zinc 

 combine with 24*8 of oxygen to form the oxide of zuic, a result 

 vhich Gay-Lussac has aho drawn from his experiments. As zinc 

 has a suboxide, and as the known oxide of this metal is analogous 

 to those which Contain more tlian one volume of oxygen, we may 

 suppose that it is Zu + 2 0, and in that case the volume of zinc 

 will weigh 80t)«43, m i.S the cise with copper and tellurium. 



'J7-, Mammnesium, vianguiiaie (Mn).— It js proved by the expe- 



