Tin. 291 



53. To find whether iron or its ore con- 

 tains manganefe, let a fmall quantity of it 

 be heated white in a crucible, and on this 

 project 5 times its weight of purified nitre, 

 taking care that no coal or aflies fhould get 

 into the crucible : when all is cold, the upper 

 part of the crucible will be covered with a 

 greenifh or bluiih cruft, if the iron contain 

 manganefe. 3 Bergm* 66. When the folu- 

 tion of iron in the marine acid is of a red 

 colour, this alfo denotes the prefence of 

 manganefe, though that colour foon changes 

 to a yellow, by extracting phlogifton from 

 the martial part. 



54. Mr. Bergman gives alfo a method of 

 finding whether the ore affords coldfhort or 

 redihort iron. He melts the regulus ob- 

 tained from the ore with J of its weight of 

 good malleable iron in a crucible lined with 

 charcoal, and well covered. If the regulus 

 thus obtained be brittle when cold, the ore 

 affords coldfhort iron, or if it cracks under 

 the hammer in a white heat, it is redfhort, 

 3 Bergm. 46, 



CHAP. VL 

 Tin. 



i . The colour of tin is too well known to 



qeecl being defcribed ; its fpecific gravity is 



U 2 fro*} 



