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brittle. On analysis Dr. v. D. PLAATS found that the grey metal 
contained 99,9 pCt. of tin and therefore was to be regarded as pure 
tin. When remelted with borax and potassium cyanide a good re- 
gulus of ordinary tin was formed. The Messrs. HAMBURGER accord- 
ingly remelted the blocks of tin in this way, including, unfortu- 
nately, a quantity which Dr. v. p. Praatrs had wished to investigate 
further. 
Of interest is further that when Dr. v. D. PLAATS mentioned the 
phenomenon to Mr. CoRNELIS DE GROOT, ex-chief of the mining 
department in the Dutch Indies, and one of the pioneers of the 
Biliton Company, he said that he was acquainted with the pheno- 
menon and added: “And it is easy to get rid of: we put such tin 
in the sun, the spots disappear in the light”. 
That the heat-rays, and not the light, are the cause of the dis- 
appearance of the spots is at once evident from the facts now and 
previously communicated. 
3. In the last paper!) (II) it was shown that the velocity of 
the reaction 
white tin — grey tin 
increases as the temperature rises from — 83° C., reaches a maximum 
at — 48° and finally becomes zero at + 20° C. 
As may be seen from the curve in that paper, the velocity 
between -+ 10° and + 20° is extremely small. In order to study 
the change in this interval of temperature it would be necessary to 
make observations lasting many years. 
On the other hand, if a piece of tin can be obtained which has 
been exposed to temperatures within that interval for a very long 
time, it is possible that it will have changed from the white into 
the grey modification. 
4. Through the kindness of Dr. W. REINDERS, at present resi- 
dent in London, and of Dr. GowLANp of London, a piece of an 
antique tin vessel, which had been dug up in England in the 
neighbourhood of Appleshaw in Hampshire, came into my possession. 
Regarding the objects found in the excavation of an old Roman 
1) Proceedings Roy. Acad. Amsterdam. 1899. Vol. Il. p. 149. 
