proceedings of the polytechnic association. 573 



Electric Light House. 



The light produced by passing an electric current generated by revolving 

 magnets through carbon pencils, is said to penetrate further through fog 

 and mist tliau that made from oil, owing to the fact, probably, that it is 

 more condensed and intense. It was first applied to a light house in France, 

 and has since been used for a similar purpose in England. 



It is not perhaps generally known that the Drummond light, so called, 

 ■which consists of the flame of oxygon and hydrogen gas, directed on a 

 piece of lime, was not invented by Drummond, but by the late Dr. Hare, 

 of Philadelphia. All that Drummond added was a reflector. The magneto- 

 electric machine used to produce light from carbon pencils, was invented 

 by Mr. Saxton, of Philadelphia. 



Cobalt Colors. 



A foreign exchange states that the readiest method of obtaining cobalt 

 yellow is to pass hyponitric acid into a solution of nitrate of cobalt con- 

 taining some potash. By addingrnore alkali from time to time, the whole 

 cobalt oxide will become cobalt yellow. This method seems to complete 

 the primary colors made by means of cobalt. The protoxide of cobalt is 

 blue, and when melted with powdered glass forms smalt. The h^'drated 

 protoxide is red. The sesqui-oxide plus 3H when cautiously deprived of 

 its water is black. The oxide intermediate these is of a dark 

 brown color. A sympathetic ink is made by a solution of the nitrate of 

 cobalt. When used on white paper, the characters are invisible in a moist 

 atmosphere, but in dry air they are red. Phosphate of cobalt oxide mixed 

 with moist alumina, and heated, produces the compound known as The- 

 nard's blue. The pigment called Rinmann's green, is a precipitate produced 

 by the action of carbonate of soda upon the sulphates of cobalt and zinc. 



Action of Light upon Leaves. 



According to the assertion of M. Corenuinder, of the French Academy, 

 leaves of alt colors absorb carbonic acid. 



Ultra-Marine. 



Prof Hoffmann, in his report upon chemical products in the international 

 exhibition, stated that within the memory of persons now living, ultrama- 

 rine, manufactured from the Persian lapis lazuli, sold for iE4, ($20) per ounce. 

 Ill 1855, there were on the continent of Europe eighty manufactories for 

 making ultra-marine artificially. Most of these are in Germany; but little 

 attention has been paid to the subject in England. The ingredients used 

 are kaolin, sulphate of soda, carbonate of soda, sulphur, charcoal, and 

 colophony. 



Silvering Glass. 



Many persons having followed the published receipts for silvering glass 

 ■without success, Mr. Joseph Dixon, of this Institute, after making a great 

 number of experiments, presents the following method as always etlcctive if 

 carefully followed: He uses four preparations: 1st. One ounce of white 

 loaf sugar dissolved in twenty-four ounces of distilled water; add to this 



