L. TECHNOLOGY. 45 7 



and steel, kilns for baking wares, etc., the idea has suggested 

 itself of coating substances otherwise incapable of resisting 

 heat with some composition that will impart to it the desired 

 quality. According to the patent of M. Ponsard, of Paris, the 

 articles in question, after having been made and dried, are 

 covered with a highly concentrated solution of chloride of 

 calcium, which penetrates the dry materials to a certain 

 depth, and is perfectly refractory. This first layer is then 

 dried in a stove, and coated with a layer of materials sus- 

 ceptible of being melted at a temperature approaching to 

 that to which the pieces will be subsequently subjected. 

 These materials are silica and clay, diluted with a solution 

 of chloride of calcium, the proportion of which varies accord- 

 ing to the temperature to which the articles made are to be 

 exposed, and to the refractory quality which it is required to 

 impart to them. These materials, on melting, form a gloss, 

 the object of which is to cover the pieces with a continuous 

 layer which protects the carbon from contact with the oxi- 

 dizing gases. 8 A, August, 1870, 152. 



DISTINGUISHING DEXTRINE FROM GU3I AKABIC. 



According to Dr. Hager, dextrine gum can be distinguish- 

 ed from gum arabic by its containing sugar. Gum arabic 

 has a per centage of lime, which causes it to become turbid 

 when mixed with oxalic acid dextrine, on the contrary, re- 

 maining quite clear under the same treatment. Gum arabic, 

 too, when added to a neutral salt or oxide of iron, throws 

 down a deposit. 9 C, January, 1871,5. 



ENAMELED IRON SLATES. 



An objection to the use of enameled iron for roofs consists, 

 it is stated, in the unequal expansion, by heat, of the metal 

 and the enamel coating, so that a fracture of the latter is pro- 

 duced. This difficulty Dr. Dingier has attempted to obviate 

 by using a more elastic coating between the metal and the 

 hard face. 8 A, January, 1871, 12. 



GABBRO MASS. 



A plastic mass, called Gabbro by its inventor, Dr. Schwartz, 

 is composed of thirty-two parts steatite, thirteen parts of pot- 

 ter's clay, and three parts of soda. The steatite is first ground 



U 



