412 On Cupellation with the Blowpipe. 
(2.) IL use also the principle of Harkort’s scale,* in measuring the 
diameters of minute cupellation globules, but applied somewhat 
differently. In most of the boxes of French mathematical draw- 
ing instruments, a brass sector scale is found, which when closed, 
shuts so as to leave, if well made, a junction that is a mere line 
to the eye. From the centre of motion, a line is drawn on each’ 
arm of the scale six inches in length, divided into two hundred 
ual parts, and when the scale is completely closed, the two 
hundreth equal part at the end of one of these lines, is exactly 
one inch from the two hundreth equal part at the end of the other 
e. 
If we wish to measure the diameter of cupellation globules, less 
than ;'; inch in diameter, (and most blowpipe globules are smaller, ) 
measure one inch between the points of the dividers, and set 
their points in the equal parts marked 195; (for ;'; inch=z$, and 
200 —5=195.) The arms of the sector scale between the points 
marked 200 are then ,’, inch apart, and approach each other to 
the centre of motion, where their distance = 0. In this way 
the scale may be set to any fraction less or greater than an inch 
that may be desired. The cupellation globule is laid between 
the diverging arms of the scale, and slidden along by a pin or 
other convenient instrument, until the globule fails in between 
the arms of the scale. The width of the opening between the 
arms at this point, gives the diameter of the globule. Suppose 
the scale set to measure globules between ,', inch and 0, and the 
globule falls in opposite the equal parts marked 45. The diame- 
ter. of the globule. is then 5: of jy =y¢deerg4y inch. ceca 
A globule of silver of 53, inch in diameter weighs about 
0-00006 grain. This weight is about + more than the actual 
weight of a cupellation globule of that diameter, because the 
above is calculated for a sphere of silver, and the cupellation glob- 
ules are always more or less flattened on the lower side, unless 
they are extremely minute. A globule of silver ;¢, inch diam- 
eter, if a sphere, would weigh 0-298665 grains; but owing to the 
flattening of the cupellation globule, the actual weight of one of 
that diameter is only 0:18 grains, or about 2 less. I do not gene 
erally permit myself to estimate the weights of cwpellation glob- 
ules by their diameters when greater than ;', inch diameter, 
consequence of the rapid variation in the law of the relative 
weights to the diameters, and globules above that. size can 
as correctly appreciated by a good balance. ‘The eye can gener- 
ally unaided by a magnifier see a globule of silver of ;s’ss inch 
diameter, which weighs about ;,552,553 grain, and this can be 
san ine ans cseea 
* Vide Whitney’s edition of Berzelius on the Blowpipe, p. 104. Px 
- tA similar method of mensuration will be found in the Appendix to Muspratt § 
translation of Plattner’s work on the blowpipe, by Prof. O, Brawe.—Lds. 
