104 Dr. J. C. Draper on an Apparatus for 



alted to such a degree that, although the strong leather belt 

 from the main shaft, used for driving the countershaft, was 6 

 inches in width and acted upon a pulley 10 inches in diameter, 

 it was scarcely able to drive the machine. 



83. It was, however, found, as in the case of the 5-inch elec- 

 tromagnetic machine, that beyond certain limits a great aug- 

 mentation of the magnetism of the electromagnet was only 

 attended by a small increase of electricity from the armature (65). 

 The results of a number of experiments, in which various quan- 

 tities of electricity were transmitted through the coils of the 

 electromagnet of the 10-inch machine, proved that when it was 

 excited through the agency of the six permanent magnets, com- 

 bined with the 5-inch machine (76), the maximum amount of 

 electricity from the machine, when working at a speed of 1500 

 revolutions per minute, had been nearly obtained. 



84. It was also found that the maximum amount of power, as 

 measured by the quantity of wire melted, was very nearly ob- 

 tained from the 10-inch machine when its electromagnet was 

 excited by means of a 5-inch magneto-electric machine alone, 

 instead of the combination of magneto-electric and electromag- 

 netic machines used for that purpose (76). 



85. When the electromagnet of the 10-inch machine was ex- 

 cited by means of the 2|-inch magneto-electric machine alone 

 (58) (as shown on the wooden top of the machine in fig. 10), 

 about two-thirds of the maximum amount of power from the 

 10-inch machine was obtained. 



XII. On an Apparatus for the Detection of Adulterations in 

 Coffee. By John C. Draper, M.D., Professor of Natural 

 History, College of the City of New York, and of Analytical 

 Chemistry in the University of New York. 



To the Editors of the Philosophical Magazine and Journal. 



College of the City of New York, 

 Gentlemen, June 1, 1867. 



HAVING been engaged during the past winter in the ex- 

 amination of specimens of adulterated coffee, I have con- 

 trived an instrument which has been of considerable practical 

 value in enabling me to obtain satisfactory results with great 

 rapidity. Thinking it may prove interesting to some of your 

 readers I enclose a description of it, which was read at a recent 

 meeting of the New York Academy of Medicine. 



It consists of a tube (a b) 1 inch in diameter and 8 inches 



