152 



Prepared silica, especially, manifests this property, if ignited at a low 

 temperature ; and, besides, takes oxides of chromium and copper from their 

 acetates, and removes certain organic matters from their aqueous solutions. 

 These reactions are more apparent in this case, because the silica is in a finely 

 divided state, chemically pulverized in fact. 



These reactions show silica to be a feeble mordant, and I think they have 

 an intimate relation to what is termed the physico-mechanical absorption of 

 soils, etc., since we thus see that one of the main constituents of rocks and 

 soils, supposed to be at once the most inert and the most insoluble in an 

 ordinary way, are capable of chemically absorbing certain substances to an 

 extent proportionate to that of the surfaces exposed ; such surfaces, even those 

 of rock-crystal itself, are certain to be in a hydrous, in fact in a pulpy state, 

 whenever water has had prolonged contact with them. It follows, therefore, 

 if a substance, which has hitherto been held to be so inert and so unassailable, 

 in these respects, as quartz, is thus actually affected in this manner, we may 

 be certain that the great bulk of our soils, and our more porous rocks, 

 have been affected by water and saline substances in a similar manner ; — we 

 may be quite certain, that the surfaces of every siliceous stone, and of every 

 grain of siliceous sand in our soils, is hydrated, and, by so far, advanced to the 

 possession of what is termed the physico-mechanical absorptive power for 

 plant-food. 



It only remains for me to state that the reactions here described tend to 

 resolve the so called "physico-mechanical absorption of soils for plant-food," 

 into a simply chemical one, or, at least, as much a chemical one as are any of 

 those undisputably recognized as such. 



Art. XXXT. — On the examination of the Bark o/"Coprosma grakdifolia, for 

 Alkaloids. By W. Skey, Analyst to the Geological Survey of New 

 Zealand. 



[Read before the Wellington Philosophical Society, July 17, 1869.] 



The sample I tested was named by Mr. Buchanan, at the time of collecting; it 

 has a bright yellow colour on its inner surface, is very bitter, with a slightly 

 hot pungent flavour. It is decidedly the bitterest of any of the barks of this 

 family, which were pointed out to me, and for this reason I made choice of it 

 for experiment. 



The following is a brief summary of the results obtained : — it shows by 

 an easy, simple, and I think a reliable process, that alkaloids, generally, and 

 those of the Quina group in particular, are either entirely absent, or present 

 only in so minute a quantity, that the bark is quite worthless as a drug, on 

 this account at least. 



A decoction of 200 grammes of the pulverized bark, in weak hydrochloric 

 acid, was slowly evaporated to a bulk of half-an-ounce, then filtered ; the 

 filtrate did not give any precipitate with the following re-agents : 

 Sulphocyanide of mercury. 

 Sulphocyanide of zinc. 

 Tannic acid. 



These substances are capital tests for the alkaloids generally, giving dense 

 precipitate in a very weak decoction, even, of the common Gray bark. 



