49 o SCIENCE PROGRESS. 



density. The Tyrolean bowls still in use at Vorospatack in 

 Hungary and in a few retired valleys in the Eastern Alps 

 do not differ essentially from the tubs drawn and described 

 by Agricola ; and, although wet crushing by the stamps has 

 been introduced, the mortar is not usually furnished with 

 screens. 



Elsewhere, the changes in stamp battery amalgamation 

 since Agricola wrote his treatise have been many and 

 great. One of the first was the addition of screens in the 

 side of the mortar, so that the two operations of crushing 

 and sifting were united. In 1767 M. Jars saw these in use 

 in the Hartz, 1 though even then only a single screen of 

 brass wire twelve inches square delivered the product of 

 three stamps, and in several other districts of Germany 

 screens had not been adopted. The most important improve- 

 ment however has undoubtedly been the introduction of the 

 amalgamated copper plate for catching gold, the comple- 

 ment of the practice of charging mercury with the ore into 

 the battery and so combining the operations of crushing and 

 amalgamation. No mention of either this practice or the 

 use of copper plates appears to have been made before 

 stamp batteries began to work in California in 1850, al- 

 though they had very likely been used in Georgia for some 

 time previously. 



The use of the copper plate was probably suggested by 

 the experience in Mexico and South America of the working 

 of the Cazo process, in which it was well known that 

 amalgam tended to adhere to the copper sides of the vessel 

 unless the proportion of mercury to gold and silver present 

 was less than four to one. Thus Baron Born wrote in 

 1786 2 : "In new kettles . . . the inside becomes wholly 

 and so perfectly silvered that it never can be cleaned. . . . 

 The silvery coat is daily increased by slow and gradual 

 apposition, and the crusts of amalgama, accumulating on the 

 bottom and sides of the vessels, become gradually so thick 

 that on emptying them they often fall off by their own 



1 Voyages Aletalhirgiques, vol. ii., p. 309. Paris, 17 So. 



2 Baron Inigo Bom's New Process of Afjialgamation, p. 1 22, Translated 

 by Raspe. London, 1791. 



