REPORT 0^ THE DIRECTOR AND STATE GEOLOGIST 1903 177 



violently. This is termed " blowing " by the workmen. It is 

 mainly for the purpose of avoiding this " blowing/' that the 

 sawdust is put in the mixture, since the former, by making the 

 mixture porous, allows the gases to escape freely. 



At the end of about 36 hours the current is cut off from the 

 furnace, and it Is allowed to cool for a few hours. Then the 

 side walls are taken down and the unchanged mixture raked off 

 the top of the furnace, till the outer crust of amorphous car- 

 borundum is reached. The crust is cut through with large steel 

 bars, and can then be easily removed from the inner crust of 

 amorphous carborundum. The inner crust is next removed with 

 a spade and the crystalline carborandum exposed. 



After the carborundum has been removed from the furnace, 

 it is taken to a crusher, which consists of a large iron pan, 

 rotated in a horizontal plane by means of a vertical shaft. A 

 horizontal shaft, carrying two heavy rollers, is attached to a 

 collar surrounding the vertical shaft, thus permitting a free 

 vertical motion of the rollers which rest in the pan. The latter, 

 in revolving, causes the carborundum to pass under the rolls, 

 which break the mass of crystals apart. From the crusher the 

 carborundum is taken to large wooden tanks, where it is treated 

 for several days with diluted sulfuric acid to remove impurities. 

 It is then thoroughly washed, dried and graded. There are 20 

 grades of crystals, from no. 8 to no. 220, the numbers indicating 

 the meshes to the linear inch of the screen through which the 

 crystals have passed. The washings from the crystals pass 

 through a series of tanks which serve to collect the fine powders, 

 and from these are made the so called " flours " and the hand- 

 washed powders. The former are obtained by floating the un- 

 graded pow^ders in a stream of water flowing through a series 

 of tanks, in which the powder settles.^ There are three grades 

 of " flour," designated, according to their flneness, F, FF, FFF. 

 The hand- washed powders are obtained by stirring up a quantity 

 of ungraded powder with water, allowing this to settle for a 

 definite time, six minutes for example, then pouring off the 

 supernatant liquid. The powder which afterward settles from 

 this liquid is called six minute powder. In a similar way other 

 hand-washed powders are made — one, four, 10 and 15 minute 

 powders. 



This artificial product is rapidly replacing garnet, emery and 



quartz in the various industries where the latter have long been 



held as superior material. Carborundum grains held together by 



^An elutriation process similar to that employed in grading emery. See 

 page 169. 



