44 NEW YORK STATE MUSEUM 



The kettle method of calcination is employed by most of the 

 local plaster manufacturers. The kettles are cylinders of boiler 

 iron from 8 to lo feet in diameter, nearly square in vertical sec- 

 tion and set upright in a brick wall. The kettle is charged through 

 a trap in the cover and heat is gradually applied, passing from the 

 fire chamber below into flues which traverse the kettle horizontally, 

 and out through a stack at the top. About lo tons of gypsum are 

 calcined in a single charge. It is necessary to keep the mass in 

 constant agitation to prevent overburning, which is accomplished 

 by means of a vertical shaft with paddles connected with the mill 

 shafting. The end temperatures range from about 350° to 400° F. 

 The rotary kiln is used in two plants ; it possesses advantages in 

 that it is continuous, requires less power to operate and is more 

 economical of heat than the kettle. The type that has been in- 

 stalled is known as the Cummer kiln. The crushed rock passes 

 through the cylinder in about 10 minutes and is discharged into 

 brick-lined bins when the calcination is completed by the residual 

 heat in about 36 hours. The plaster is then ground. 



The calcined plaster in part is converted into wall plasters, plas- 

 ter board, etc., and partly sold as stucco. Wall plasters are made 

 from plaster of paris by the addition of some retarder, an organic 

 or mineral substance which delays the time of setting, and of a 

 fiber, such as hair, shredded wood or asbestos. Plaster boards are 

 formed of layers of paper cemented with plaster of paris. 



IRON ORE 



The year 1909 was characterized by extreme fluctuations in 

 the iron trade. During the first few months market conditions 

 were little better than in 1908, which was a year of unreUeved 

 depression. The mining companies were unable to contract 

 for more than a fraction of their normal output and conse- 

 quently operated on a small scale. There was even then a 

 considerable surplus of ore which had to be stocked. By the 

 middle of the year the market had experienced a decided im- 

 provement which finally brought an end to the long depression. 

 Mining was then resumed at the usual rate and for the re- 

 maining months the demand for ore was sufficient to keep the 

 mines running at their maximum capacity. 



The output reported by the mines was 991,008 long tons 

 valued at $3,179,358. This was practically an increase of 

 300,000 tons over the product for 1908 which amounted to 

 697,473 long tons valued at $2,098,247. The total fell somewhat 

 short of the output in 1907 but with this exception was the 

 largest reported in any year since 1891. The average value of 

 the ore was $3.21 a ton against $3.01 a ton in 1908. 



