316 PROF. HARRISON AND MR. JUKES-BROWNE ON [Aug. J^O^, 



lenger ' Report on Deep-Sea Deposits, p. 430. The material was 

 dried at 230° F. :— 



Loss on ignition 4 - 50 



f Alumina 6"00 



i Ferric oxide 9*77 



t-, ,. i ui • Calcium phosphate - 48 



Portion soluble in , T -j r. no 



hvdroohloric acid J Manganese oxide 0'68 



Calcium sulphate - 42 



Calcium carbonate l - 69 



Magnesium carbonate 1*33 



Silica 24-95 



fAlumina 1T37 



Portion insoluble j Ferric oxide 2'00 



in hydrochloric ■{ Lime ..., 114 



acid=50 - 18. j Magnesia 0"85 



^ Silica 34-82 



100-00 



It will be seen that this analysis gives no real indication of the 

 mineralogical composition of the clay. This is owing to the method 

 employed, which is stated by Dr. Brazier himself to be as follows * : — 

 ' The deposits in these analyses were treated as earths by me, and, 

 after digestion in hydrochloric acid, were evaporated to dryness and 

 subsequently re-dissolved as far as possible ; the insoluble residue, 

 after weighing, was treated with boiling caustic potash, and so much 

 of the residue as was then dissolved was looked upon as silica of easy 

 combination, and classed along with the bodies soluble originally in 

 hydrochloric acid.' 



It is difficult to see what object was gained by this proceeding, or 

 why silica only soluble in boiling caustic potash should be classed as 

 ' soluble in hydrochloric acid,' as it is in all the printed analyses. 

 In order to ascertain for ourselves what the effect of digestion in 

 hydrochloric acid would be, we digested 5 grams of the ' red clay ' 

 with 10 per cent, hydrochloric acid over the water-bath for 12 hours, 

 and then found that we had 16-93 per cent, of silica soluble in alkalies, 

 j^ext we boiled a like amount of clay with strong hydrochloric acid 

 as long as the acid attacked the clay, and we then had 26*22 per 

 cent, of silica soluble in alkalies. As Dr. Brazier made 24-95 per cent, 

 of silica soluble, it may be assumed that he digested the material with 

 strong hydrochloric acid for a similar length of time. The result was 

 simply to decompose a larger portion of the silicates and to mask 

 the actual amount of soluble organic or colloid silica present. It 

 will be seen from our analysis that the amount of this colloid silica, 

 derived from radiolaria, diatoms, and sponge-spicules, is only 4-61 

 per cent. 



The next point to be noticed is that the alkalies were not determined 

 by Dr. Brazier, but in the published analyses are either included 

 under the head of ' insoluble silica ' or else with some other con- 

 stituent, the amount of which was determined by difference, but is 

 not indicated. In our detailed analyses we found the total amount 



1 Quoted by Dr. Murray, ' Challenger ' Report on Deep-Sea Deposits, p. 29. 



