Assaying is the estimation of the amount of pure metal, and especially of the precious metals, in an ore or alloy. In the case of silver the assay is either by the dry or by the wet process. The dry process is called eupellation from the use of a small and very porous cup, called a cupel, which is usually made of well-burned and finely-ground bone-ash or of magnesia. The cupel, being thoroughly dried, is placed in a fire-clay oven about the size of a drain-tile, with a flat sole and arched roof, and with slits at the sides to admit air. This oven, called a muffle, is set in a furnace, and when it is at a red heat the assay, consisting of a small weighed portion of the alloy wrapped in sheet-lead, is laid upon the cupel. The heat causes the lead to volatilize or combine with the other metals, and to sink with them into the cupel, leaving a bright globule of pure metallic silver, which gives the amount of silver in the alloy operated on. In the wet process the alloy is dissolved in nitric acid, and to the solution are added measured quantities of a solution of common salt of known strength, which precipitates chloride of silver. The operation is concluded when no further precipitate is obtained on the addition of the salt solution, and the quantity of silver is calculated from the amount of salt solution used.
An alloy of gold is first cupelled with lead as above, with the addition of three parts of silver for every one of gold. After the cupellation is finished the alloy of gold and silver is beaten and rolled out into a thin plate, which is curled up by the fingers into a little spiral or cornet. This is put into a flask with nitric acid, which dissolves away the silver and leaves the cornet dark and brittle. After washing with water the cornet is boiled with stronger nitric acid to remove the last traces of silver, well washed, and then allowed to drop into a small crucible, in which it is heated, and then it is weighed. The assay of gold, therefore, consists of two parts: cupellation, by which inferior metals (except silver) are removed; and quartation, by which the added silver and any silver originally present are got rid of. The quantity of silver added has to be regulated to about three times that of the gold. If it be more the cornet breaks up, if it be less the gold protects small quantities of the silver from the action of the acid. Where, as in some gold manufactured articles, these methods of assay cannot be applied, a streak is drawn With the article upon a touchstone consisting of coarse-grained Lydian quartz saturated with bituminous matter, or of black basalt. The practised assayer will detect approximately the richness of the gold from the colour of the streak, which may be further subjected to an acid test. The Goldsmith's Company of London is the statutory assay-master of all England. Research Assaying
A vapour trail is a trail of condensed water vapour that appears in the wake of an aircraft or rocket at high altitude. Vapour trails appear as a white streak, like long, thin, regular clouds, against the sky and quickly broaden and disintegrate. Research Vapour Trail
The Berkshire is a breed of English pig. It is black with white feet and a white streak or star on the forehead. It has a short, thick nose; arched back; short legs and its belly near the ground. It is more suitable for bacon than pork. Research Berkshire Pig
The puma (Felis concolor) is a large wild cat found in the Americas where it is often also called a panther, painter, cougar and catamount. Next to the jaguar, the puma is the largest American cat, and once ranged from New England and British Columbia to Patagonia. In the adult the upper surface is a uniform tawny colour, except for a dark streak along the middle of the back, and a dark tip to the tail, while the under surface is of a paler tint. he presence in the young, however, of a ringed tail and of spots on the body shows that the puma's ancestors possessed characteristically feline colouration.
Pumas vary greatly in size, sometimes reaching 2.5 metres from nose to the tip of the tail, the tail being usually about a metre long, but usually the body is about a metre long. The puma lives in low-lying plains and on mountain slopes both in forests and in treeless pampas where it feeds on larger animals, typically horses, sheep, deer, larger rodents, birds, rats, mice and fish. Research Puma
The wheatear (Saxicola oenanthe) is a genus of chat birds. The male is greyish blue above, with a black streak at the side of the head, the wings are nearly black, the rump white, the tail black and white, the under surface white with a tinge of buff. The food consists of insects and the bird is commonly found on moorlands near the sea. The nest is often built in rabbit holes or in the crevice of a stone wall. Research Wheatear
Creeping eruption is a skin disorder characterised by a progressing red streak caused by a hookworm larvae burrowing under the skin. Research Creeping Eruption
Blue Streak was a British inter-continental ballistic missile project following the Second World War. The launch sites were deemed too vulnerable to enemy attacks and the project was cancelled at the end of the 1950s. Research Blue Streak
A touchstone is a device for roughly ascertaining the purity of gold alloys. It consists of a smooth strip of hard black stone, on which a corner of the alloy is rubbed so as to leave a streak, which is then moistened with an acid composed of 78.4% nitric acid, 1.6% hydrochloric acid and 20% water. By comparing the effect with that produced on streaks made with alloys of known compositions, an approximation to the gold content of the alloy is found. Research Touchstone
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Research Assaying
