606 Mr. J. Y. Buchanan on Chemical Work 



manganate of potash be added to a sample of it, and let the carbonic acid 

 be determined in the usual way by boiling the solution. If the water 

 contained any easily oxidizable carbon compound, we should obtain more 

 carbonic acid in the second than in the first determination, and the differ- 

 ence would correspond approximately to the amount of organic carbon 

 present. In several waters which I have treated according to this prin- 

 ciple, I have found from two to five milligrammes of carbon per litre. 



Observations on the occurrence of Manganese Nodules on the Sect-bottom. 



Occasionally pieces of stone of a black colour have been brought up, 

 and been found to consist of peroxide of manganese mainly. Several 

 interesting specimens were obtained between Bermuda and the Azores, 

 which were apparently steps in the formation of the black substance out 

 of concretions of the bottom at the place in question. They were 

 obtained on the 17th and 27th Jane, and may be divided into four 

 classes : — 1st, those which contain no manganese at all ; 2nd, those where 

 the manganese formation has commenced ; 3rd, those where it is well 

 advanced ; and 4th, those where the bulk of the substance is peroxide 

 of manganese. Those of the first class are, as far as can be learned from 

 qualitative analysis and microscopical examination, merely mechanical 

 aggregations of the bottom existing at the place in question. Of a 

 white colour, and generally the same appearance, are those of the second 

 class ; they contain, however, numerous perforations, whose walls are 

 lined with a very thin black film peculiarly striped. On treating with 

 dilute hydrochloric acid, the mass is found to consist chiefly of car- 

 bonate of lime with a considerable quantity of clay. Strong hydrochloric 

 acid decomposes the latter, when a certain amount of chlorine is given off. 

 In another concretion, belonging to the same class, the manganese is seen 

 forming in minute mammillary concretions on the outside surface, as well 

 as on the tube linings. Belonging to the third class is one (also brought 

 up on the 27th June) where the outside is wholly covered with oxide of 

 manganese ; and in cutting through the substance of the stone, the layer 

 is seen to be of a sensible thickness ; also all the worm-holes are seen to 

 be completely coated ; and numerous more minute holes are found, all of 

 which are coated in the same way. A very considerable percentage 

 of the whole mass has thus become manganese. On the face of a fresh 

 cutting the interior of the mass may be seen to preserve its white colour. 

 From the edge of the black layer inwards, however, the mass is stained 

 of a brownish colour, which gradually disappears towards the centre. 

 Blackish brown veins are also seen to traverse the whole mass. Pulverized, 

 it effervesces strongly with dilute hydrochloric acid. The residue is 

 easily decomposed by strong acid, evolving large quantities of chlorine ; 

 silica is left undissolved with a little sand. In the hydrochloric-acid 

 solution there was found, besides alumina, manganese, and a little iron, 

 a certain quantity of nickel and cobalt. A concretion of the fourth class 



