i873«] Technology. 281 



a circuit of given resistance, it should be necessary that the resistance of the 

 magnetising helix should equal that of the exterior circuit — have shown that 

 the conditions of sensibility admit of a much greater length of wire than 

 would correspond to the resistance of the exterior circuit. His calculations 

 and experiments prove the maximum to be obtained with helices presenting 

 twice the resistance of the exterior circuit. 



M. Benoit has found the initial resistance in steel and iron to be doubled at 

 170 ; in silver, copper, and gold, at 255 ; in platinum, at 455 . In alloys the 

 increase is generally more feeble ; in standard alloy, for example, the resistance 

 is increased at 86o° by only 0*3 of the value at zero. The coefficient of ex- 

 pansion was carefully taken into account. 



Dr. Blake, of the San Francisco Academy of Sciences, announces the dis- 

 covery of a current of electricity running north and south, at a distance of 

 about 150 miles from the Pacific coast, along a belt of metallic deposits, 

 serving as a conducting-chain. 



TECHNOLOGY. 



It is estimated that there from 20,000 to 25,000 persons in Europe daily 

 engaged in the preparation of hair and the manufacture of felt hats, in which 

 processes they are exposed to mercurial poisoning. M. Hilairet, in experi- 

 menting on this subject, impregnated skins with a neutral substance, as 

 molasses, or dextrine, or sugar, then put them in nitric acid, and found that 

 by the action of the nitrous and hyponitric acids thus developed, the hair un- 

 derwent a change of structure corresponding exactly to that obtained by means 

 of the solution of mercury in nitric acid. 



Von Scherzer, who first introduced to Europeans a varnish made by the 

 Chinese, by beating together fresh blood and quick-lime, and used to make 

 wooden articles completely water-tight, states that he has seen in Pekin 

 wooden chests, which have been varnished with it, and after a journey 

 "over Siberia to St. Petersburg and back, were still sound and perfectly water- 

 tight. Baskets of straw, used for the transportation of oil, are made fit for 

 the purpose by means of this varnish ; it also gives the appearance and 

 firmness of wood to pasteboard coated with it. Articles required to be ab- 

 solutely impervious are varnished twice, or at the most three times, by the 

 Chinese. 



M. Hallwachs asserts that not only green, but red carpets also contain 

 arsenic, particularly the brilliant dark reds now so much in vogue. Samples 

 of these carpets burned with the blue arsenic flame, gave off the characteristic 

 garlic odour. Enough colour to give a distinct arsenic reaction could be 

 rubbed off with the finger. A solution in hydrochloric acid produced the 

 usual greyish precipitate of metallic arsenic. 



A few years ago an oil well was started near Cumberland, Maryland ; but 

 instead of striking oil, the pioneers came upon a gas chamber and penetrated 

 it. The gas was ignited and continued burning. About a year ago, Mr. 

 Haworth, of Boston, purchased the well, and obtained a patent for the manu- 

 facture of carbon. The gas is allowed to burn against soapstone plates, on 

 which the carbon is deposited in the form of soot. Six hundred and sixty 

 burners are now in operation, each burner consuming 8 cubic feet per hour. 

 By a mechanical arrangement, the soot is scraped and deposited in large 

 tin boxes about 3 feet long, i£ feet wide, and i\ feet deep; scrapers are passed 

 along the soapstone plates every twenty minutes, and the boxes are filled on 

 their fourth passage. A building, twice the size of the present one, is now 

 in course of construction. It will have in use 1328 gas burners. The present 

 consumption of gas amounts to about one-twelfth the whole quantity escaping 

 from the well. The total consumption of gas by the burners of both buildings 

 will be one-fourth of the whole. The carbon is generally used for the manu- 

 facture of ink. 



The following is a description of the process for preparing alcohol from 

 sawdust : — Into an ordinary steam boiler, heated by means of steam, were 



