ON THE CHEMICAL PROPERTIES OF SILK. 153 
Nitric acid has a strong influence upon silk ; and, 
if mixed with aleohol, changes silk to a permanent 
bright golden yellow colour. The same acid, when 
concentrated and distilled off silk, yields by evapo- 
ration oxalic acid; and if the evaporation is still 
farther continued, the same acid, together with a 
quantity of yellow octohedron-sided truncated crys- 
tals are obtained. These are free from an acid 
taste, but of a strong bitter, and if applied to the 
skin leaves a deep yellow stain. When the re- 
maining liquor is saturated with potash, and eya- 
porated, the residue is a rather yellow salt, which 
detonates when placed on live coals, like nitre. 
Chemists suppose this to be a treble combination of 
the bitter principle above mentioned, together with 
nitrate of potash. 
Silk is dissolved and corroded by the caustic 
alkalis; and chlorine renders it yellow. It 
yields a greater quantity of yolatile alkali than 
almost any other substance. It was found by 
Tournefort to contain even more than hartshorn, as 
he obtained from fifteen ounces of silk two drachms 
of volatile salt. This preparation was at one 
time in high repute in England as a medicine ; 
and was called English Drops, or “ Gutte Angli- 
cane.” The cocoons of silk were reduced into a 
powder by Pomet, and used as a medicine. In his 
History of Drugs he says, that silk thus prepared had 
VoL. IIL. L 
