CE/FFIx's FCRNAUE. 



CHEMISTRY. 



307 



or against fusion with the clay. The crucible is to be 

 covered by the plumbago jacket, Fig. 29. The space 

 Fig. 24. 



Fig. 25. 



between this pile in the centre of the furnace and the 

 two cylinders, e e, which form the walls of the furuace, 

 is to be filled with flint stones, or gravel, washed clean 

 and dried. The stones which answer best are rounded, 

 water-worn pebbles, of half an inch to one inch diameter. 

 These may be piled up to the top edge of the jacket, 

 Fig. 29. The number of clay plates must be such as to 

 bring the top of the crucible to the distance of two 



Fir. 20. Fig. 27 



Fig. M. 



Fig. 29. 



inches, or two-and-a-half inches at the utmost, from 

 the flat face of the gas-burner, a. In some cases, 

 merely one of the furnace cylinders, e, is necessary ; in 

 which case the crucible and its jacket is placed directly 

 upon the cylinder, Fig. 27 ; and wheu ouly a moderate 



Fi. 30. 



Fi|f. 31. 



heat is require: 1, i:\vn the packing with pebbles may be 

 dispensed with. Another means of diminishing the heat 



is that of increasing the distance between the gas-burner 

 and the crucible. 



In Fig. 20, it will be seen that the gas-flame is 

 driven, by means of the blast, directly on to the crucible. 

 Another illustration represents that form of the furnace 

 in which the heat is produced beneath the crucible. 

 (See Fig. 30). 



The packing of this variety of furnace is performed 

 as follows : The clay plate, d, is placed upon the tripod- 

 stand. The crucible jacket, Fig. 31, or one similar, but 

 of larger size, is placed upon the plate, d. The crucible 

 and its cover is then put into its place, and is covered 

 with the dome, Fig. 32, which must rest upon the lifter, 

 /, and must be of such a width as to clear the crucible 

 easily when lifted. The internal height of the dome 

 should be such as just to clear the top of the crucible 

 cover. Consequently, where crucibles of different sizes 

 are used, domes of different sizes are also necessary. 

 Observe, distinctly, that the crucible and its support are 

 to rest upon the plate, d, and the dome upon the 

 lifter, /. The furnace cylinders, e e, are now to be 

 superposed, and the space between the dome and the 

 cylinders, and that above the dome, are to be filled 

 with small pebbles, as already directed. The gas may 

 then be lighted ; the blast of air set on ; and the opera- 

 tion be allowed to proceed. 



Fig. 33 represents a plumbago crucible, which is used 

 to suspend the inner crucible over the gas- pi g . 33. 

 flame. By means of such a furnace, six 

 inches in diameter, three pounds of copper 

 or cast iron can be fused in a quarter of an 

 hour. From eight to ten pounds of copper 

 or cast iron can be melted in an hour's 

 time ; and thus a portable and almost in- 

 stantaneous source of intense heat is afforded. 



The chemist requires various kinds of crucibles for 

 his purposes. The student may supply himself with a 

 few of the Hessian and English kind ; and, for more 

 delicate experiments, those of Berlin porcelain are to be 

 preferred. Occasionally, a platina crucible is used ; and 

 it should always be placed in a Hessian one if employed 

 in a furnace in which coke or charcoal is used. This 

 precaution is unnecessary if a gas furnace be employed. 



Hi-id. -s the apparatus already mentioned, bottles for 

 containing chemicals, stirring-rods, and a variety of 

 minor articles, which will suggest themselves, will be 

 required, which can be supplied at leisure. We must 

 not omit to name, that some glass tubing, from an eighth 

 to a quarter of an inch in diameter, is extremely useful, 

 and can be readily converted to many purposes. The 

 following are directions for bending it into any form 

 that may be required. For tliis purpose, soft tubing 

 should be used. A piece of the proper length is to be 

 cut off by means of a file ; and the part that is to be 

 bent must be held in the flame of a spirit or gas-lamp 

 by the ends, until it is sufficiently softened to bend 

 easily. The further ends are then to be gradually 

 I'd downwards, care being taken that the red-hot 

 portion is not bent into an angular form, but that a 

 nmnd edge is preserved, in shape similar to the letter U. 

 If this be not attended to, the bent tube will almost 

 certainly break at that part. Pieces of glass tube may 

 be joined together by means of india-rubber connections;* 

 or if the end of one piece be heated red-hot, and slighbiy 

 inlaid by means of a piece of iron run round it, the 

 end of the other piece may then be inserted, and the 

 two fused together at a red heat, or by means of a 

 common blowpipe. After a little practice, the student 

 will be able to work readily with glass, providing it be of 

 the soft kind. German glass tubes cannot bo so easily 

 managed, because they do not soften except at high 

 temperatures. 



We shall conclude our remarks on manipulation and 

 apparatus, by urging on our readers the following pre- 

 cautions, if they desire to pursue chemistry successfully 

 and economically. And first, it is of great importance 

 that cleanliness be observed. An apparently clean glass 

 may be chemically speaking, very dirty ; for some tests 

 See antt. p. 305. 



