1878.] *$*■ [KOnig. 



determination. Some of them are eminently chromatic as : Manganese 

 cobalt, vanadium, titanium, and they are capable of very accurate determi- 

 nation. 0. m s r - 01 of Mn.,0 ,, dissolved in lOOmgrs. of borax glass yields a 

 distinct color, 0. m &- 1 a deep color, 0. ra s r - 2 nearly opaqueness. The range 

 of greatest sensitiveness is between 0. m s r - 05 and 0. m s r - 10 ; the limit of un- 

 certainty for my eye is 0. msr - 002 Mn. 2 ... 



Execution of the method. 



1. Preparation of the bead. Before starting upon an analysis, I melt a 

 number of borax beads weighing each about 90 mgrs. Some of these I 

 crush in a steel mortar and keep the coarse powder on a watch glass for 

 use. A number of platinum wires, weighing 100 mgrs. each, or a few 

 tenths ltss, are likewise kept in readiness. They have at one end a cir- 

 cular loop (I) 0.1 inch in diameter. One of these wires O), Fig. 1, I place 

 on the pan of a delicate balance, which should indicate one twentieth of a 

 milligram with precision, and at the same time rapidly. (Such balances 

 are known as "Small size Assay balances and are manufactured in great 

 perfection by the firm of Trimmer & Sons of Philadelphia.) The 

 wire is readily tared by the milligram rider, as its weight is close to 

 100 mgrs. — A quantity (s) of 5 ragr. of the finely ground ore, or in many 

 cases of determinative mineralogy a splinter of a mineral, is now weighed 

 with the greatest care (the hand must rest exactly at zero) since an error 

 here of ± 0. mgr - 05 will produce either 99 percentum or 101 instead of 100. 

 With some practice the error will not exceed ± 0.5 p. c. I remove now 

 the 5 mgr. weight and replace it by one decigram. In the other pan I 

 place one of the ready borax beads (5) and with the addition of pulver- 

 ized borax glass (p) equilibrium is restored. The scale pans are made of 

 platinumfoil. The one holding the flux and substance is placed on a holder 

 (Plattner's cupel holder is very good) and brought beneath the blowpipe 

 flame, so that the current of gases will not affect it, whilst the wire is in- 

 serted into its handle. The flame is a strong clean oxydizingone, produced 

 best with lard oil and a mechanical blast (I find a small Catalan blast, 

 made from a Wolfs bottle, very convenient and steady). Bringing the red 

 hot loop of the wire down upon the borax bead causes this to adhere firmly, 

 and after being melted picks up at once and without loss the smaller par- 

 ticles of the flux. In adding now the substance every precaution against 

 mechanical loss must be taken. Should the substance contain volatile 

 matter, care is particularly required, because if the mass of red hot flux be 

 dipped into the midst of the fine powder the gases or vapors will generate 

 so suddenly that a scattering must take place. But if the bead be ap- 

 proached to the margin of the small heap of powder and only a small 

 quantity of it be taken up at a time, no loss will be sustained, as many ex- 

 periments prove. From the smooth platinum surface of the pan every par- 

 ticle of substance can be collected. This operation consumes from 5 to 10 

 minutes according to the solubility of the metallic oxides. The bead is 

 now allowed to cool and, still on the wire, replaced on the balance. Some 



