662 Transactions of the American Institute. 



ocular demonstration of the operation of the physical laws of 

 cstronomy. When put in motion, by means of a hand crank, it 

 shows the relative position and motions of the earth, moon and 

 inferior planets, for every second, with the phenomena of conjunc- 

 tions, transits, eclipses, nodes and phases of the moon, the eccen- 

 tricity of its orbit, as well as that of Venus and Mercury, &c. The 

 sphere representing the earth is covered with a map of the two 

 hemispheres, surrounded by a meridian and equator, which always 

 maintain their true relative position to the sun. Instructors, by its 

 use, may give their scholars a clear idea of the changes of the 

 seasons, and of the length of days and nights in different latitudes, 

 and other interesting astronomical phenomena. 



SEPARATION OF TIN AND ARSENIC. 



Professor Wohler's method is based on the solubility of sulphide 

 of arsenic in bisulphate of potash, which does not dissolve the tin. 

 The mass, after being oxydized by nitric acid, is allowed to digest 

 with sulphur and caustic potash till the solution is complete. The 

 liquid, after being treated by sulphurous acid in excess, is allowed 

 to rest for some time, and is then evaporated until all the sulphu- 

 rous acid is driven off. The sulphide of tin is then removed by 

 filtration, and washed with a strong solution of common salt, which 

 may be removed from the precipitate by an acid solution of acetate 

 of ammonia. The sulphide of tin is converted into oxyd of tin by 

 roasting in contact with air. Arsenic may be precipitated fi'om 

 the arsenious acid contained in the liquid, by a current of sulphu- 

 retted hydrogen. 



CURE FOR DRY ROT IN WOODEN STRUCTURES. 



Mr. Junker, the manager of the alkali works at Saaran, in Silesia, 

 has discovered that tank- waste, the great nuisance of all alkali 

 works, is an excellent remedy against dry rot in wood. This kind 

 of decay is the work of the spores of a fungus {mendus lacrymans), 

 which generally find their way through the soil, and are sometimes 

 carried by currents of air. The tank-waste is said to arrest their 

 action in half decayed wood. It may be used by mixing with other 

 material, so as to form a solid mass, which will harden like the 

 ordinary tank-waste floor. If the mixture called tank-waste is the 

 soda-waste described in chemical works, it is chiefly composed of 

 calcium compounds, about one-third of soda waste being oxychloride 

 of calcium. In England, where the business of making soda-ash 

 and pure carbonate of soda is carried on more extensive|jF than in 



