One of the great advantages common to all systems of chlorination is that ores may be crushed dry and treated, so that the loss from float gold may be avoided.  Of this loss, which is most serious, we shall have something to say on another occasion.  An advantage in amalgamation with chlorine gas instead of amalgamation with quicksilver in the wet way, is that the ore need not be crushed so finely.  Roasting takes the place of fine crushing, as the ore from the roasting furnace is either found somewhat spongy in texture or the grains of silica in which fine gold may be incased are split or flawed by the fire.  For quicksilver amalgamation very fine crushing is necessary to bring all gold particles in contact with it.  Quicksilver being so thick in substance, it will not find its way readily in and out of a microscopically fine spongy body or through very fine flaws in grains of silica, whereas chlorine gas or a solution of liquefied chlorine does this, and absorbs the gold far more readily.

There are cases when gold is contained in ores in what is known as a perfectly “free” form—­that is, there is an absence of all sulphides, arsenides, etc.—­when it is not practicable to extract it either with the ordinary forms of quicksilver amalgamation of or any process of chlorination, without first roasting.  This is because the finer gold is locked up inside fine grains of silica and hydrated oxide of iron.  No ordinary crushing will bring this fine enough, but when roasting is resorted to by drawing it rapidly through a furnace heated to a cherry red, these grains are split up so that chlorine gas is enabled to penetrate to the gold.

It may be said that an equally clever chemist will be required to work this improved process as compared with those that have, one by one, fallen into disuse, mainly from want of knowledge among the operators.  To a certain extent this is so.  The natural chemical actions are not so delicate, but an ignorant operator would spoil this process, as he does nearly every other.  When a reef is discovered, practice shows that its strongest characteristics are consistently carried throughout it wherever it bears gold.  Before Messrs. Newbery and Vautin leave a purchaser to deal himself with their process, they get large samples of his ore to their works and there experiment continually until a practically perfect result is obtained; then any one with a moderate amount of knowledge can work with the formula supplied.  It has been their experience that the ore from any two mines rarely presents the same characteristics.  Experiments are begun by treating very coarse crushings.  These, if not satisfactory, are gradually reduced until the desired result is obtained.