SCIENCE NOTES.

Digger (Invercargill RSA), Issue 37, 26 November 1920, Page 13

SCIENCE NOTES.

THERMOMETER DETERIORATION. Even thermometers become old, and consequently inaccurate with age, mercurial instruments reading too high and spirit instruments too low. In the former case the bulb appears to shrink, thus forcing the quicksilv.er too far up the stern. This gradual shrinkage is supposed to be due to the fact that the extemal pressure cn the bulb may be considerably higher than the internal pressure, the air as far as possible having been removed before the glass is sealed off. On the other hand, the spirit thermometer is sealed with the bulb covered in a freezing mixture, in order to lock up in the glass as much air as possible. The instrument thus starts with an internal pressure which in time appears to he reduced either by expansion of the glass under the internal pressure or by the leakage. TIN RECOVERY. The recovery of tin from scrap has engaged the attention of several chernists, especially since the demand for the tetrachloride of tin has been increased by the rapid growth of the use of silk. A new process has just been patented in which the scrap tin is first treated with a strong solution of sodium hydroxide at from 120de.g. to 150deg. F. in an iron tank lined with graphite or some other material electfo-negative to tin. The galvanic action set up between the graphite and the tin accelerates the solution of the tin, and the operation is repeated with various batches of scrap until the hath is rich in tin. The solution is then placed in a second iron tank and bales of scrap tin are suspended in the bath and a current passed. The tank J acts as the cathode and the tin becomes j the anode. In this process the tin from the bale is dissolved and deposited, while the tin is also deposited from the bath itself, so that it can be retumed to the first tank and re-usedv CARBON BLACK. Carbon black is a fluffy, velvety pigment, usually produced by burning natural gas with a smoky fiame against a metal surface and the product is . entirely different from lamp black, with which it is sometimes confused. Lamp black is gray in comparison with carbon black and in all plac.es where carbon black is used, lamp black is practically an unsatisfactory substitute. In normal times the Lnited States has been in the habit of exporting about 15,000,000 pounds and besides this has used in printers' ink ten to twelve million, ruhber goods. twenty millibn ; stove polish, four to five million ; and miscellaneous, one million pounds annually. The United States Bureau of Mines has undertaken an investigation of • probable sources oi' lamp black and with the gradual lessemng of the natural gas supply the question of carbon black may hecome a rather serious one. The present methods are known to rccover but a few per cent. of the carbon in the gas, and development. work on efficient methods of production from natural gas and other possible materials is in order. The thermaLdecomposition of gas or other hydrocarbons with insufficient supply of air, or explosion with carbon mbnoxide, carbon dioxide, oxygen or their mixtures has been suggested.