162 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



ened. For the glass jar, the author furthermore substitutes a 

 wooden box of the same size, coated with a mixture of wax, 

 two parts ; resin, ten parts ; red-lead, two parts ; and gypsum, 

 one-sixth part. 1 A, XXXI., 203. 



SIMPLE METHOD OF MAKING CARBON CELLS. 



Mr. Symons gives the following method, as practiced by 

 himself, for constructing plates or cells of carbon of any re- 

 quired shape and size, such as are used in galvanic batteries. 

 With a sirup of equal quantities of lump sugar and water, 

 mix wood charcoal, in powder, with about equal parts of the 

 light powder called vegetable black. The mixture should 

 hang well to the moulds dipped into it, and yet be suffi- 

 ciently free to form itself into a smooth surface. Moulds of 

 the cells required are made of stiff paper, and secured by wax 

 or shellac. These moulds are dipped into the carbon sirup, 

 so as to cover the outside only, and then allowed to dry. 

 This dipping and drying ought to be repeated until the 

 cells are sufficiently thick ; when well dried they are buried 

 in sand, and baked in an oven hot enough to destroy the 

 paper mould. After being cleared from the sand and burned 

 paper, the cells are soaked for some hours in diluted hydro- 

 chloric acid, and again well dried, then soaked in sugar 

 sirup. When dried, they are packed with sand in an iron 

 box, gradually raised to a white heat, and left to cool. If 

 some of the cells be cracked, they need not be rejected, but 

 covered with paper or plaster and dipped into melted paraffin. 

 Rods or plates of carbon can be made by a similar process. 

 The carbon thus made will be found to have a 2*ood metallic 

 ring, and a brilliant fracture. 12 A, XL, 8. 



NEW ABSOLUTE GALYAXOMETEE. 



An absolute galvanometer is described by Professor Guth- 

 rie, as constructed for him by the Messrs. Elliott. Its princi- 

 ple consists in the determination of the strength of the cur- 

 rent, by the measurement of the mechanical force necessary 

 to bring: to within a given distance of one another two 

 electro-magnets which are affected by the current in such 

 a manner that they repel one another. The galvanic cur- 

 rent whose force is to be measured coils around two fixed 

 soft iron masses, rendering them magnetic, and then around 



