80
JOURNAL OF CHEMICAL EDUCATION
JANUARY, 1930
mentals of electrochemistry, will doubtless soon find a place in every laboratory where this subject is taught. This will probably be one of the first scientific instruments which pupils will endeavor to have introduced into the technical laboratories. Some of the other instruments which have been described, for measuring H-ion concentrations and conductivity, are just as suitable for industrial measurements, and they are gradually coming into favor for such use. It appears highly desirable that the pupils in electrochemistry become familiar with these instruments, in order to be familiar with their use when they enter technical laboratories, as well as to encourage their introduction. When instruments have been made to be direct reading in the desired units, and when their manipulation is simple, they are no longer laboratory playthings but practical eqnipment for the industrial laboratory.
Rare Earth Elements in Glass. Professor Weidert, of the Kaiser Wilhelm Institute for Silicate Research of Berlin, and director of the technical optics laboratory of the Berlin Technical High School, recently discussed the use of the rare earth elements as components of glass. He pointed out that one gram of neodymium or praseodymium cost 20 marks before the war, but was now much cheaper. Didymium glass was used during the war for secret optical telegraphy. Glass containing cerium was used in spectacles t o cut out ultra-violet light, p d zirconium was used in the produdion of cloudy opal glass. Neodymium glass is especially suitable, by insertion before mercury vapor lamps, for the production of monochrodtic light. This method deserves introduction in all investigations in which monochromatic light is indicated, which have hitherto been carried out with sodium light, e. g., in the sugar industry. Neodymium makes red or green appear sharper; i t may, therefore, be used t o correct incomplete color-blindness. Recently, neodymium and praseodymium have been applied extensively in the manufacture of art glasses. I n these, the color depends on the thickness of the glass, so that parts of varying thickness show a changing play of colors; and the glass is, therefore, used in the production of artificial gems. The color also depends on that of the incident light; for example, praseodymium glass is green in daylight and colorless in candlelight.-Chem. Age Dehydrated Tartrate of Lime. A new product, dehydrated tartrate of lime, known as "supertartrate," and containing from 73 to 78 per cent of tartaric acid, is now being produced from wine lees by the SocietC Industrielle de Languedoc a t its Saint-Laurentd'Aigouze plant. The Societe Alsacienne des Produits Chimiqnes d'Alilsace is installing a t its Vaugouin plant, a t Rochelle-Palice, equipment far the dehydration of ordinary tartrate, and its transformation into supertartrate. This ordinary tartrate will be furnished to the plant by a series of local plants which the company is installing in the departments of the Tarn, Aude and Pyrenees-Orientales for the extraction of tartrate from distillation residues. It is reported that the Societb Industrielle de Languedoc is engaged in negotiations for the cession of its patents and processes abroad for the production of supertartrate; and in America, for the production of tartaric acid with supertartrate as a hasis.-Chem. Age
