284 ZINC - 



as a moderately astringent and stimulant application in some forms 

 of cutaneous eruptions, ring-worm, sore nipples, and chronic 

 inflammation of the conjunctiva, depending on a relaxed state of 



the vessels. 



Impure Oxide of Zinc, or Tutty. Oxidum Zinci impurum, 

 E. Tuttia, D. — The nature and origin of this substance has not 

 been well ascertained. According to Dr. Murray, it consists of 

 oxide of zinc with argillaceous earth, and is supposed to be an 

 artificial compound, prepared from the sublimed oxide of zinc 

 that collects in the chimneys of the furnaces in which the metal is 

 roasted, mixed with clay and baked. It is of a grey or brown 

 colour, and earthy texture, and, when levigated, it is used for the 

 same purposes as calamine. 



Salts of Zinc. 



Nearly all the acids act with energy on zinc, and form salts 

 some of which have been used in medicine. They are, in general, 

 soluble in water, and their solutions are colourless. They are de- 

 composed by the alkalies, and afford white precipitates] with 

 sulphuretted hydrogen and the ferro-prussiate of potash. 



Sulphate of Zinc. Zinci Sulphas, L. E. D. — This salt is pre- 

 pared by pouring diluted sulphuric acid on zinc, and evaporating the 

 solution so far that, on cooling, the sulphate is obtained in acicular 

 crystals. In this process, the metal combines with the oxygen of 

 the water and with the acid, a sulphate of zinc being formed while 

 hydrogen gas is disengaged. It is usually prepared on a large scale 

 from the common sulphuret or blende. The ore is roasted, wetted 

 with water, and exposed to the air. The sulphuret attracts oxygen, 

 and is converted into sulphuric acid ; and the metal being at the 

 same time oxidized, combines with the acid. After some time, the 

 sulphate is extracted by solution in water ; and the solution being 

 evaporated to dryness, is run into moulds. When procured in 

 this way, it generally contains a small portion of iron, and some- 

 times of lead. This salt, known in commerce under the name 

 of white vitriol, is said to have been discovered in Germany about 

 the middle of the 16th century. The form of its crystals is that 

 of flat quadrangular prisms, terminated by four-sided pyramids. 



