Prof. Chapman on the Assaying of Coals by the Blowpipe. 433 



long), and the glass index to which the needle is attached. A 

 small piece of fine copper wire attached to the needle hangs 

 within a groove cut in the wooden block. By means of a hole 

 pierced horizontally from the back of the instrument, entering 

 about midway down the groove, a stud can be made to press the 

 fine copper wire against the anterior wooden block (that not 

 seen in the figure). By doing this the needle and pointer (pre- . 

 viously let down by turning the roller so as to slacken the silk 

 filament) are held securely. The instrument can then travel 

 safely, and the experimenter is saved the otherwise inevitable 

 trouble of suspending the needle afresh at the journey's end. 



In the instrument I have got fitted for Mr. Gordon, 2798 

 yards of No. 40 silked copper wire are wound on a reel 4 inches 

 in diameter, the object being to obtain an effiect accurately mea- 

 surable with a very small quantity of current. But coils of dif- 

 ferent lengths and sizes of wire can be readily attached to the 

 instrument. Although the silk filament is only li inch long, and 

 the needle is little more than a quarter of an inch long, the tor- 

 sion is so trifling that an entire twist of the filament deflects the 

 needle only one degree from the magnetic meridian. The resist- 

 ance presented by the air to the motion of the glass pointer, 

 stops the oscillations of the needle in about half a dozen seconds. 



T 



LIV. On the Assaying of Coals by the Blowpipe. By E. J. 

 Chapman, Professor in University College, Toronto*. 



IHE blowpipe had been employed with great success for 

 nearly a century in the examination of minerals and che- 

 mical products, with a view to distinguish these numerous bodies 

 from one another, and also to ascertain their general composi- 

 tion, when Edward Harkort of Freiberg first appHed it to the 

 quantitative investigation of certain silver ores and furnace pro- 

 ducts. Plattner, who had worked with Harkort, subsequently 

 extended this application to the assaying of various metallic sub- 

 stances, and added in no small degree to the utility of the in- 

 strument, by the invention of new methods of research, and 

 many new appliances, published collectively in his well-known 

 Probirkunst mit dem Lothrohref. No one, however, has yet 

 attempted to employ the blowpipe in the practical examination 



* Communicated by the Author. 



t This work reached in 185;:t its fourth edition. Harkort's earlier publi- 

 cation (1827), of which, however, merely the first i)art was issued, bore a 

 similar title. P'or all that concerns the history and general application of 

 the blowpipe, the reader may consult the fourth edition of the standard 

 work by Berzelius, as translated by Whitney. A new edition of this work, 

 incorporating the various tests and discoveries published since the death of 

 its distinguisiied author, is much required. 



