266 Scientific Intelligence. ; 
burner is unadvisable in quantitative analysis, since by means of it the 
weight of platinum crucibles is altered and the crucibles themselves in- 
j The coating is produced most rapidly when the crucible is placed 
in the inner cone of the flame, and the more readily in proportion as the 
pressure under which the gas is burned, is higher. Having found it ad- 
vantageous to maintain, by means of a special small gas holder, a pres- 
sure of four or five inches upon the gas used in his own laboratory, Erd- 
mann has observed that the strong gas flame thus afforded, immediately 
becomes red hot; it increases continually so that after long continu 
ignition the whole of the bottom of the crucible will be found to be gray, 
and with its lustre dimmed. 
This ring is caused neither by sulphur, as some have believed, nor by a 
coating of inorganic matter, but is simply a superficial loosening of the 
texture of the platinum in consequence of the strong heat; whence it first 
In conjunction with Pettenkofer, Erdmann instituted several experi- 
ments which have left but little doubt that the phenomenon depends upon 
not increased. The 
bisulphate of potash or with carbonate of soda. It disappears, however, 
when the metal is polished with sand ; the loss of weight which the cru- 
cible undergoes, being exceedingly insignificant, a crucible weighing 25 
grams, having lost hardly half a milligram. hen the gray coating of 
the crucible is examined under the mieroscope it may be clearly seen that 
the metal has acquired a rough, almost warty, surface, which disappea's, 
when it is polished with sand, Platinum wires which are frequently 
ignited in the gas flame, for example the triangles which are used to sup- 
as is g i Under the micro 
scope they exhibit a multitude of fine longitudinal cracks which as the 
original superficial alteration penetrates deeper become more open, or a8 
| 
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