538 M. Wiederh old on Solid Hydride of Arsenic. 



Some of these crystals are of a blue colour, so dark that they 

 would be considered black, but that the intensity of the colour is 

 somewhat less at the edges. 



Lamellar Rutile. — When titanic acid dissolved in fluosilicate of 

 potash is heated to bright redness in a current of hydrochloric 

 acid, lamellar crystals of rutile are obtained resembling the 

 natural rutile of New Jersey. 



Sagenite. — A mixture of titanic achl, silica, and fluosilicate of 

 potash, heated in a current of hydrochloric acid, gives rise to a 

 number of small needles planted edgewise in a skeleton of silica. 

 In their colour and shape they present an undoubted analogy 

 with the Sagenite of Saussure. 



Brookite is obtained in transparent very fragile plates by heat- 

 ing to dull redness a mixture of titanic acid, silica, and fluosili- 

 cate of potash in a current of hydrochloric acid. There is no 

 silica in the crystals, and their density and shape identifies them 

 with the Brookite of St. Gothard. 



Black crystals of Arkansite are obtained when the preceding 

 experiment is made in a crucible of gas-charcoal. 



When fluotitanate of potash is heated in a current of dry 

 hydrogen charged with a small quantity of hydrochloric acid, 

 the bifluoride of titanium liberated is reduced to protofluoride of 

 titanium, which crystallizes in beautiful prisms of a deep violet 

 colour. 



When acicular rutile is prepared in a charcoal crucible, the 

 mixture being heated for some time before passing the current 

 of hydrochloric acid, blue crystals are obtained containing 5 per 

 cent, of fluorine. The colour produced is due to the presence of 

 protofluoride of titanium . 



Some of these syntheses are not new. Rutile has been 

 obtained crystallized by several methods, but none of them have 

 given the complete series of these varieties of the mineral. 



Wiederhold* has described a method for preparing the solid 

 hydride of arsenic, which was first obtained by Davy, by passing 

 an electrical current through water and using arsenic as the 

 negative pole. Davy also observed that when arsenide of potas- 

 sium was treated with water, hydride of arsenic was left as a 

 brownish-red powder. It has been stated that when arsenide of 

 zinc is treated with hydrochloric acid, hydride of arsenic is left : 

 Soubeiran showed that the residue is an insoluble alloy contain- 

 ing excess of arsenic. Wiederhold has now shown that, by taking 

 an alloy of special composition, the hydride may be obtained. 

 In preparing this alloy, which consists of five parts of zinc and one 

 of arsenic, certain precautions are necessary, and especially that 

 * PoggendorfFs Annalen, April 1863. 



