312 Scientific Intelligence. 
“The definite proportions I regard as a maximum toward 
which the chemical fo es strives, a maximum from which the 
deviations in most cases af Pa although in others they may be 
very large; and I sucaie that this view of the subject, which 
the memoir has aimed to Tabak: is supported by the analogies of 
re. 
e shown ina slag memoir that these numbers” (the 
Greaea oe law, not ana sha lite e agreem ment with it, the differ- 
ences be 
een the theoretical and the experimental pi yl: 
pee | in las cases too great to be Leake by errors of obse 
zs 
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2: 
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_ retical equivalent may be the ecwten towards which the chemi- 
cal force tends.” 
oe In a subsequent paper entitled “Crystalline Form not necessa- 
a rily an Indication of Definite Chemical Composition, or on the 
- Possible Variation of Constitution in a Mineral Species in gree 
_ ent of the Phenomena of Isomorphism,” published in the hilo- 
 sophical Magazine (June, 1860), during a it t to London, the — 
- ; ‘witer. shows that ——. e lanatio may be Ee of t ne ce 
eue no iets pee his rigen aed ole to, oe ee 
_ been directed to the exact point in question, and in none of the 
analytical results which have been more recently cited as possi ae 
examples of variation in the combining proportions has it beep 
conclusively shown that the discrepancies may not result from 
ow. 
a uring the last twen nty-five years, however, a more ext nded 
ps Anowledzs has been acquired of that class of indefinite eh chemical 
ek fe which like the alloys seem to occupy an 
positi n betw ween definite Semper on and ects ” eel oe 
example as many of the hydrates and silicat tes 
nal Boe the limits between chemical an 
e case of the « line comport 
