Everyman's chemistry; by Hendrick Ellwood

Author:Hendrick, Ellwood. [from old catalog]
Language: eng
Format: epub
Tags: Chemistry
Publisher: New York and London, Harper & brothers
Published: 1917-03-25T05:00:00+00:00

EVERYMAN'S CHEMISTRY

oxides (rust) from surfaces which are to be soldered. The equation given above shows how hydrochloric add is liberated, which does the work. Like all salts of zinc, the chloride is astringent and i>oisonous. ''Bamett's Disinfecting Fluid," so called, is a solution of zinc chloride.

Zinc sulphate, ZnS04, is a white salt, known also as white vitriol. It is used in industry and in medicine for external applications. A }4 P^ cent, solution is used in certain eye affections.

Tin, —^If the elements had consciousness, tin would need a group of eminent counsel to defend it from charges of irregularity. It has two methods of combining—with two bonds and with four. As tin, tinnic, and tinnous compounds did not sound just right to the chemical authors, or possibly they <Ud not know whether to speU the adjectives with one **n" or two, they took the Latin word stannum and made their adjectives of that. Stannous compounds are of tin with two bonds, while stannic compounds indicate that four bonds are engaged.

Tin is addicted to allotropy in the worst way. It is a silver-white, crystalline metal of low tenacity but great malleability under ordinary conditions. It also retains its luster on exi>osure to the air. It is soft enough to be cut with a knife but harder than lead, while not so hard as zinc. Despite its great ductility, which is greatest at about loo*^ centigrade (the boiUng-point of water), it grows brittle enough to be pulverized when it has been heated up to 200*^. If a bar of tin is bent, it emits a low, crackling noise, called the "tin cry," said to be due to the rubbing of the crystal faces, one upon the other. It has a great disposition to crystallize on solidification into

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two different forms of crystals according to conditions, tetragonal and rhombic.

Now if this same tin is cooled to a low temperature it will crumble to a gray powder. This takes place very slowly at ordinary cold-weather temperature, but is likely to proceed very rapidly at —48*^ centigrade. At temperatures lower than this the crumbling slows down. Organ pipes and roofs have been observed to go to pieces from this "tin pest," or '*tin disease," as it is called. If a piece of tin in process of change from its metallic state to the gray-powder form is brought into contact with ordinary white tin, the "disease" will catch. And all the while it is neither more nor less than tin. These forms are merely its allotropic modifications.

It is fotmd in Cornwall, England, in the Malay Archipelago, in Bolivia, Australia, Bohemia, and Saxony. The usual ore is tinstone or cassiterite, and is stannic oxide, SnOs, combined with the arsenical, copper, and other mineral sulphides and tungstates. There is also a comparatively rare tin pjoites, being sulphide of tin, copper, iron, and sometimes zinc. The ore is smelted, and the resultant metal is about 99>^ per cent. pure.

It dissolves in hydrochloric add to stannous chlor'de

Sn + 2HCI « SnCli + H|.

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