BOOK XXXIV. XXVI. iii-.xxvii. 114 



prefer to grind copper filings mixed with vinegar 

 in copper mortnrs. But the quickest result is 

 obtained by adding to the vinegar shavings of 

 coronet copper. Rhodian verdigris is adulterated 

 chiefly with pounded marble, though others use 

 pumicestone or gum. But the adulteration of 

 verdigris that is the most difficult to detect is done 

 with shoemakers' black," the other adulterations 

 being detected by the teeth as they crackle when 

 chewed. Verdigris can be tested on a hot fire- 

 shovel, as a specimen that is pure keeps ^ its colour, 

 but what is mixed with shoemakers' black turns red. 

 It is also detected by means of papyrus previously 

 steeped in an infusion of plantgall, as this when 

 smeared with genuine verdigris at once turns black. 

 It can also be detected by the eye, as it has an evil 

 green colour. But w^hether pure or adulterated, the 

 best way is to wash it and when it is dry to burn it 

 on a new pan and keep turning it over till it becomes 

 glowing ashes ; and aftervvards it is crushed and 

 put away in store. Some people burn it in raw 

 earthenware vessels till the earthenware is baked 

 through ; some mix in also some male frankincense. 

 \^erdigris is washed in the same way as cadmea. § 106. 

 Its powerfulness is very well suited for eye-salves 

 and its mordant action makes it able to produce 

 watering at the eyes ; but it is essential to wash it 

 ofFwith swabs ^ and hot water till its bite ceases to be 

 felt. 



XXVII. Hierax's Salve is the name given to an 

 eye-salve chiefly composed of verdigris. It is made 

 by mixing together four ounces of gum of Hammon,'^ 



variety of common salt, which itself is not sal ammoniac = 

 ammonium chloride). 



211 



