C hap. 2 9. ] Medical Preparations of Iron. 173 



'tin in a proper proportion, it enables the manufacturers 

 to lay on a thinner coat of tin without injury to the co- 

 lour. This practice, however, is rather of prejudice 

 to the duration of the plates. When the tin is heated ' 

 to a great degree, the covering which it imparts to 

 the iron is thinner but more even. The plates are 

 apt, from this caufe, to have yellow fpots on them ; 

 but this inconvenience may be removed by boiling 

 the plates for two or three minutes in lees of wine, 

 or, where they cannot be had, four fmall beer, or other 

 fimilar fluids, may probably be ufed with the fame 

 fuccefs. 



. Iron is juftly confidered as a valuable article of the 

 materia medica, and while its utility is confiderable, 

 it is entirely free from thofe deleterious and debilitat- 

 ing effects which proceed from moft of the other 

 metals that are ufed as medicines. The ferrum vi- 

 triolatum, or green vitriol, has been already men- 

 tioned. The ferri fubigo is made by merely expofing 

 iron filings to the air, and moiftening them with water 

 till they are converted into ruft. The ferrum tarta- 

 rifatum is prepared by mixing one part of iron-filings 

 with two of cry dais of tartar moiftened with water, 

 and expofing them to the air for eight days. In this 

 preparation the iron is chiefly brought to the faline 

 (late by means of the acid of tartar. The ferrum 

 ammoniacale, or flores martiales, is made by mixing 

 one pound of iron filings with two of fal ammoniac, 

 and applying a brifk heat. The fal ammoniac fub- 

 lims and carries up fo much of the iron as to be 

 changed to a deep orange colour. The flores mar- 

 tiales may be made equally well with the colco- 

 thar of martial vitriol as with the iron-filings. The 

 tinctura ferri ammoniacalis, or ammoniacal tinc- 

 ture of Iron, is made by digefting one pint of proof 



ipirit 



