GOLD TESTING

Hokitika Guardian, 29 October 1932, Page 6

GOLD TESTING

SECRET PROCESS DOUBTED. CHRISTCHURCH, Oct. 27, The statement made by a witness, in the Supreme Court yesterday thaJ thorn was a secret process lor. .testing gold, which could not be divulged, was not supported by some city jewellers and gtld buyers this morning. One buyer, however, stated that there was a secret process, which would do great harm to the trade if it became known to the public.

Dr h. Denham, Professor of Chemistry at Canterbury College, said tnai the only quick test he knew of as suitable for gold buyers was that in which a- touchstone and nitric acid

wore used. A suspected piece of geld was i'utilled along a touchstone, ana the smear tested with acid. Then a piece of gold of known standard was rubbed along the stone; by comparing the coloration of the two metals caused by the action of the acid, a true and quick test of genuineness was ava~ able.,

The specific gravity test, while longer and more painstaking, was accurate to a degree, continued Professor Denham. The specific gravity of gold of a certain carat was known, irrespective of its weight. By . taking . the specific gravity of dubious metal, or of ‘‘faked” medals such ns were shown in tile Supreme Court, the fraud would be at once shown up. ‘

A jeweller described the quick test for gold which is applied in the shop, when artilces come in for sale. The gold is taken and filed fairly deeply. Then nitric acid is applied to the cut. The jeweller watches the action of the acid on the metal, and runs his finger over the spot where the acid rests.

If the gold is of nine carat, it turns a dark colour; if the metal is slightly tinted with brown, it,is of 15 carat; and if of .18 carat (almost pure) there will be no discolouration. In this way it is easy to form an estimate of the price, as different rates apply for gold of different carat. Nitric acid will not attack pure gold. It can only bo acted upon by aqua regia, n mixture of nitric and hydrochloric acids. Should the riietal thought fie turn green under the nitric acid, then the jeweller knows that if there is any gold present, it has been alloyed with brass, copper, silver or other metals. The specific gravity test is not used by jewellers to any great extent, because it takes too long. Gold is classified according to its fineness in carats, pure cold being known as 24 carat; The English standards are 22. 18, 15. 12 and 9 carats, hut other countries have tlieir own standards o r purity. A greenish alloy used by goldsmiths contains 70 P°r cent siliver and 30 per cent golc\. “Rule gold” has 75 per cent gold and 25 per cent iron, while 'many other alloy-s have beqn ev.Q.lred to suit- certain uses of the metal.

The British sovereign and halfsovereign, first introduced in 1817, consist of eleven parts of pure gold, and one part of an alloy, usually copper or silver. .The sovereign is 22 carat gold. ' ■