801 



angle of (lie oj)lic'al axes 2F=iabout 357,°- tor cristobalite theso 

 values arc: //^zz= 1,484, and 7iy = 1,487. 



The Uthiumoxide : Li J) is only sparely known up to llii.s dale, 

 A description of it is to be found in an instructive paper of L. 

 Troost '), whose data we in general could confirni. lie obtained (lie 

 oxide from lithiumcarbonate, by healing it at a high temperature in 

 the presence of coal in a platinum-crucible, and also by heating the 

 nitrate of lithium in silver crucibles at a i-ed heat. The burning of 

 lithium in oxygen gave only partial results, as the [)rotoxide: LiJ)^ 

 was formed. The presence of this peroxide causes the yellow colour 

 of the product. Troost describes the IJ^O as a white compound, 

 with cristalline rupture. We prepared the pure oxide after the method 

 of De Forcrand -), l\y heating lithiumcarbonate in a platinum vessel 

 at 830° — 900° C, while a current of dry hydrogen is run over it 

 continuously. We obtained in this way an absolutely white, cristal- 

 line product, which makes the impression of having been melted. 

 This however is not the case, as the aspect is caused by the melting 

 of the carbonate itself before its decomposition. For, as we found, 

 the oxide does not melt under these circumstances, but can sublime 

 already under 1000° 0. 



We were able to contirm Troost's observation, that pure. Li J) 

 does not attack the platinum, even at very high temperatures, but 

 that the metal is attacked however, as soon as the oxide is heated 

 with it in an oxidizing atmosphere. The cause of this phenomenon 

 is the resulting peroxide, which attacks the platinum most intensily, 

 and gave to it the yellow or olive-green colour, which we have also 

 observed, whenever the lithiumorthosilicate was heated with 

 the metal. The view of the French author, that in absence of oxygen, 

 the hi^O can be heated to a very \\v^\\Q\\\\)^v\\X\\vQ,iintho at melting, 

 is also quite right. We have made some experiments, to determine 

 its raeltingpoint by means of the use of the "hollow thermoelement", 

 — a method to be described further on, in the study of the 

 orthosilicate and the mixtures, rich in Li^O. It was found then, that 

 a heating to 1570° 0. (about 16400 M.V.) caused only a baking 

 together of the powder to a very hard mass, which was coloured 

 slightly yellowish by a trace of Li^O.,, formed from Fa J) and the 

 small quantity of air, present in the platinum-bulb; however even 

 now the mass was probably not yet molten, nor at 1625° C, as we 

 found afterwai'ds. Because the platinum is very soft at these tempe- 



1) L. Troost. Ann. de Chim. et do Phys. (3). 51. 144, (1857). 

 -) De Forcrand. Compt. rend. 144. 1402, (1007). 



