98 ANNUAL OF SCIENTIFIC DISCOVERY. 



RESHARPENING OLD FILES AND RASPS BY A CHEMICAL PROCESS. 



THE London Chemist states that, by the following cheap and simple 

 process, old files and rasps may be made nearly equal to new ones. 

 First boil them in soap lyes, or a mixture of slacked lime and soda in 

 water ; this done, wash them in water, and directly throw them into 

 a tub full of dilute sulphuric acid, formed of one part acid and six 

 parts water; let them remain here for some time, the exact period 

 being easily found by taking out a file and observing whether the 

 nicks appear sharp or not ; as soon as the desired sharpening is effect- 

 ed, the files must be taken out and washed in another tub containing 

 a solution of soda, about an ounce of soda to a pail of water. 



CLEANSING OF METAL CASTINGS. 



IN the old process of cleansing of metal castings, by water contain- 

 ing sulphuric or hydrochloric acid, the coating is more or less per- 

 fectly removed, but the surfaces are left rough and unequal. Messrs. 

 Thomas and Delisse found that the coating was removed from cast 

 surfaces with great certainty, when, to water acidulated with sulphu- 

 ric acid, organic matter, such as glycerine, artificial tannin, naphtha- 

 line, creosote, or stearine was added. This acid liquor does not dis- 

 solve the coating, but detaches it, and causes it to scale off, leaving 

 untouched the metal below. By this process, which is peculiarly 

 applicable to the cleansing of zinc and brass, sixty per cent, of acid is 

 saved, and not half as much metal lost as in the old process. But 

 the organic substances mentioned above being difficult to procure in 

 many instances, M. Eisner applied himself to discover some cheaper 

 and more easily procurable organic matter which would answer as 

 well, and he has found that both wood and coal tar answer perfectly 

 well. A piece of iron casting was immersed in a mixture of tar and 

 dilute acid, and was completely cleansed, without any disengagement 

 of hydrogen gas, the surface being left of a clear, grayish-black color, 

 quite clean and smooth, and totally unattacked by the acid. A simi- 

 lar casting immersed in the solution ordinarily used in this process 

 was almost wholly dissolved in an equal time. Technologiste. 



ALLOYS OF MANGANESE AND IRON. 



DR. JACKSON exhibited to the Boston Society of Natural History, 

 in January, several specimens of white cast-iron containing manga- 

 nese. The iron was remarkably crystalline and brittle, and resembled 

 in color pure antimony. Specimens containing five per cent, of man- 

 ganese crystallized into broad lamellae, and cleaved readily into crys- 

 talline forms. Specimens containing nine per cent, were more highly 

 crystalline, with broad plates of crystals intersecting each other, giv- 

 ing the broken surface of the pig the appearance of meteoric iron that 

 had been acted on by acids. The specific gravity of the first spe- 

 cimens was 7.684 ; of the second, which contained three per cent, 

 more manganese, 7.488. In specimens containing sixteen per cent. 



