Intelligence and Miscellaneous Articles. 415 



Fcrrocyanide of potassium produces in solutions of the tantalates 

 of the alkalies, when they have been rendered slightly acid, a yellow 

 precipitate ; in those of the pelopates, a brownish-red ; and in those 

 of the niobates, a red one. 



When the three acids are fused with bisulphate of potash, they 

 dissolve in it. Niobic acid alone solidifies with it to a crystalline 

 mass. Water removes sulphate of potash from the fused masses, 

 and leaves compounds of sulphuric acid with the metallic acids, 

 from which however the sulphuric acid can be removed by very long 

 treatment with water. 



When hydrochloric or sulphuric acid is added to the solution of 

 the niobate of potash or soda, and then a bar of zinc immersed in 

 it, the separated niobic acid soon assumes a very beautiful pure blue 

 colour. It gradually becomes dirtier, and finally brown. The blue 

 colour is produced, in the solutions of the alkaline pelopates, only 

 on the addition of sulphuric acid ; but not even then is a blue colour 

 produced in the alkaline tantalates, which however takes place when 

 the solution of the chloride of tantalium in sulphuric acid is treated 

 with water and zinc. 



Tantalic acid yields before the blowpipe colourless pearls with the 

 fluxes even in the inner flame ; pelopic acid gives with the microcosmic 

 salt in the outer flame a colourless, in the inner one a brown pearh 

 Niobic acid colours the microcosmic salt in the inner flame of a 

 beautiful blue ; the pearl can be easily blown colourless in the outer 

 flame. 



These are the most important differences between pelopic acid 

 and tantalic acid on the one hand, and niobic acid on the other. To 

 ascertain accurately the behaviour of these acids and their combina- 

 tions is one of the most difficult tasks, as all three acids frequently 

 exhibit highly anomalous properties. We have seen, for instance, 

 that the niobic acid is readily dissolved, under certain circumstances, 

 by hydrochloric acid, when separated from its combinations, while 

 under not very dissimilar circumstances it is almost entirely precipi- 

 tated by it. This is owing to the acid assuming different isomeric 

 modifications. 



The three acids resemble in this respect uilieic acid, the behaviour 

 of which towards reagents is frequently remarkable, and only excites 

 less surprise from our having been long acquainted with this acid, 

 and its properties having been thoroughly examined. 



This tendency of the three acids to assume different isomeric 

 modifications is connected with the great variability which they 

 exhibit with respect to their specific gravity. My experiments on 

 this subject have led me to the most unexpected results ; although 

 I have not terminated my investigations, I will nevertheless commu- 

 nicate at present some of the most important. 



Some time ago I drew attention to the fact, that in the artificially 

 prepared titanic acid the specific gravity gradually increases by 

 long-continued ignition, until it attains that of rutile. In the same 

 way the modifications of titanic acid which occur in nature, anatase 

 and brookite, may be converted by continued ignition into rutile. 

 I thought that the publication of these facts would have induced 



