THE BEGINNINGS OF PH0T06EAPHY. 335 



solutivo water) prepared ])y distillation of a mixture of vitriol of 

 Cyprus (copperas), saltpeter, and alum. By adding- sal ammoniac a 

 kind of aqua regia was formed, which he says would dissolve gold, 

 sulphur, and silver. B}' dissolving calcined silver in its solutive water 

 (nitric acid), and allowing a third part to evaporate, he ()l)tained the 

 nitrate in the form of small fusi))le stones, like crystal. (Invention of 

 Verity, cap. 2, p. 266.) He also mentions a peculiar celestine or 

 h3^acinth color produced ])y exposing* silver to the fumes of acute 

 things — as of vinegar, sal ammoniac, etc. Later on we find a g-reat 

 many references to this silver blue pigment in the writings of the early 

 chemists and painters. In some cases the color was no doubt due to 

 the verdig]-is formed by the action of strong vinegar on the copper 

 alloy mixed with the silver, l)ut in others it may have been a form of 

 chloride or compound chloride of silver with ammonia and copper of 

 an intense blue color. So that silver chloride may have taken its place 

 in pictorial art very much earlier than is generally supposed. Entzelius, 

 in his De Re Metallica (Frankfort, 1557, p. 17), mentions a plum col- 

 ored silver ore which, according to Theophrastus, was used as a tine 

 pignuMit. He also notes the great variet}^ of color shown by the ores 

 of silver. 



We may pass over Albertus Magnus and the alchemists of the 

 eleventh to the fifteenth centuries, whose methods of making nitric 

 acid, silver nitrate, and at^ua regia were for the most part derived from 

 Geber. And though they must have been acquainted with silver 

 chloride, they have, so far as I have been able to ascertain, h^ft no 

 record of the action of light upon it or an}" other silver compound. 

 Little, indeed, to this effect can be found in the works of the earlier 

 mineralogists and metallurgists of the sixteenth century, who mention 

 several different ores of native silver, but seldom undei- the name of 

 horn silver, or luna cornea, and it is very difficult to ascertain which 

 of the many translucent ores descril)ed by them really was tlie native 

 chloride. 



One of the earliest and 1)\' far the most important of these writers, 

 Georgius Agricola (Georg Bauer), in his De Natura Fossil ium, liber S, 

 written al)out 1546, mentions silver as producing black lines and dirty- 

 ing the hands; acids also corrode it, tinge it l)lue, and destroy it. In 

 another passage, in liber 10 of the same work, he describes an excellent 

 method of making- the blue pigment al)Ove referred to by exposing 

 sheets oF sihcr full of small iissures, which should be filled up with 

 mercury, to the vapors of a mixture of sal ammoniac dissolved in the 

 strongest vinegar in a closed vessel buried in the earth or in dung for 

 about twenty da3^s. 



The l)est edition of his Dc Re Metallica and other works, published 

 at Iksel in 1657, is a complete treatise on mining and metallurgy, 

 illustrated with many curious pictures of mines and mining machinery. 



