ULTRAMARINE, ARTIFICIAL. This substance, which is chiefly composed of sulphide of sodium, is extensively used in the arts, particularly by paper makers for giving a blue tint to paper. There is a very large manufactory of it at Dusseldorf, where some hundreds of men and women are employed. The following is the account of the process, as described by Dr. Redwood.
" Mix together 1 part of porcelain clay, 1 a part of sulphur, 1 part of anhydrous carbonate of soda, and keep the mixture at a dull red heat in a covered crucible as long as vapours are given off. On opening the crucible it will be found to contain a spongy mass part of which will be of a dark-blue colour, and this is to be sepa rated from the other part. The results of this proce,ss are not uniform, yet it is considered the best that has yet been published." Since photographic prints are readily destroyed by an alkaline sulphide, it is evident that the above colouring matter should on no account be added to photographic papers, and yet all the foreign papers manufactured for photography are tinted with it.
URArnim. U=60. This metal is obtained from the mineral
termed Pechblende, which is an impure oxide of it, and also from uranitic mica. The process consists in acting on the oxide with potassium. It is obtained as a black powder which has a powerful affinity for oxygen. The protoxide of uranium was for some time mistaken for the metal itself, and is not by any me,ans a costly substance.
There are five oxides of uranium, viz. :— Suboxide . . U4 Os Protoxide . . . 0 Black oxide . . U4 06 Green oxide . . . U8 04 Peroxide .
Sesquioxide . . U2 03 Uranic acid.
The protoxide is a grey or brown powder obtained by passing hydrogen over peroxalate of uranium at a red heat. The salts of the peroxide are reduced to salts of the protoxide by the action of light, as in the case of the iron persalts, so that in this respect uranium and iron are analogous. The hydrated peroxide is a yellow powder.
Unemum GLASS. Glass is frequently coloured yellow by the addition of oxide of uranium. It possesses the property bf " Fluo rescence," q. V.