338 THE BEGINNINGS OF PHOTOGRAPHY. 



From the sixteenth centuiy onward the science of chemistry as dis- 

 tinct from alcheni}', or the search for the philosopher's' stone and 

 transmutation of metals, beg-an to develop in connection with medicine 

 under the impulse of the teaching of Paracelsus and his followers. 

 Tinctures of gold and silver being considered of high remedial value, 

 attention was paid to the preparation of salts of these metals. It is in 

 a book of this kind, the Basilica Chymica, by Oswald Croll (Frank- 

 fort, 1608), we have perhaps the first distinct mention of the precipita- 

 tion of silver chloride by adding salt water to a solution of silver in 

 aqua fortis. He mentions its fusibility, softness, and capability of 

 being cut b}^ a knife, and calls it, from its horn-like appearance after 

 fusion, "that unknown luna cornea,*" and warns his readers against 

 it being used in combination with lead to prove the transmutation of 

 metals, the falsified lead being apparently turned into silver. He 

 says nothing, however, about an}" darkening in light. 



In the translation of Erckern's book on Assa^dng, by Sir John 

 Fettus (Fleta Minor, 1683), page 5, he refers to the horny ore of silver 

 as being called so from its transparency, or rather lucidation, like 

 horn, and very rich in silver next to certain glass ores, or sulphides. 

 In the same way, C. K. Schindlcr, in Dcr Geheimbde Miinz (luardein 

 und Berg Probierer (1705), mentions horn ore as a kind of transparent 

 ore like the horn of a lantern and of rich yield. 



That these horny ores of silver were identical with the luna cornea 

 or horn silver, formed by fusing the precipitated chloride, seems 

 doubtful from the account of them given by J. A. Cramer in his 

 Eleinenta Artis Docimasticic (1739), of which there is an English trans- 

 lation by Dr. Cromwell IVIortimer (1764). Horny silver ore is described 

 as semitr^nsparent, of a deeper or lighter yellow or brown color, 

 according to the size of the pieces, looking like resin, easily powdered, 

 and lamellar in structure. When strong]}' heated it emits sulphurous 

 and arsenical fumes and only contains two-thirds of silver. 



In the second part of the l)ook he describes the purification of silver 

 by precipitation as chloride with nuiriatic acid from the solution of the 

 nitrate. If the precipitate is dried and melted and poured out quickly 

 "it appears as a body of a light scarlet color, half transparent, pon- 

 derous enough, and so tenacious that it is diflicult to reduce it to pow- 

 der, and if you'})reak it, it seems to be of a fi})rous texture within; 

 whence it is called 'Lunje cornua,' on account of its resembling the 

 horns of animals on the outside." He, however, says nothing about 

 this substance ]>eing darkened by exposure to light, nor of its relation 

 to the horny silver ore. 



CRONSTEDT AND WOULFE. 



We find the first distinct recognition of the identity of the true 

 hornertz, or horny silver ore, with the luna cornea, or horn silver, pre- 

 pared by precipitation from the nitrate in Cronstedt's essay toward a 



