In all ore dressing and milling Operations, including flotation, cyanidation, gravity concentration, and amalgamation, the Working Principle is to crush and grind, often with rob mill & ball mills, the ore in order to liberate the minerals. In the chemical and process industries, grinding is an important step in preparing raw materials for subsequent treatment. In present day practice, ore is reduced to a size many times finer than can be obtained with crushers. Over a period of many years various fine grinding machines have been developed
WASHING THE PRECIPITATE: A precipitate may be washed directly on the filter, or it may be washed partly by decantation and partly on the filter. If by decantation, the precipitate is allowed to settle, and the supernatant liquid is poured on the filter. Wash water is added to the precipitate, and after settling, the decantation is repeated a few times, and finally the precipitate is transferred to the paper or Gooch crucible.
Whatever method of washing be used, it must be thorough; and that this may be so, both the precipitate and the paper or asbestos must be washed free from all traces of
Material of Vessels for Solution
The student must consider the effect of the solvent used on the vessel. In most cases the solvent used is an acid or mixture of acids, and for such solvents glass and porcelain are generally used. Platinum may be used, provided no chlorine or other attacking agent be present. (See notes regarding care and use of platinum crucibles.) For strong alkalies silver or nickel vessels should be used, as glass is attacked sensibly by hot and even cold solutions of caustic potash or soda, and porcelain is also attacked to some extent.
Methods of Solution & Apparatus used
When a substance is soluble in water
Analytical Balance Principle
In this place it will be sufficient to describe the usual chemical balance, designed to carry in each pan a load up to 100 gms. This balance can be obtained at a reasonable figure, and sensitive to 1/10 of a milligram (0.0001 gm.). In the section on Assaying the student will find two other forms—Pulp Scales and the Assay Balance— mentioned. The pulp
Scales are cheap, and sensitive to about 1/100 gm., and serve well for weighing quantities of 20 gms. and over. The assay balance is more sensitive than the chemical balance, but its range is shorter (from .5 gm. to .00005 gm.). The student who
FIG. 35 gives an idea of the spectroscope and of its different parts. P is a flint glass prism, having a refracting angle of 60° and resting on a brass plate fixed on a brass support, S. The brass plate carries the collimator tube C, in the end of which nearest to the prism is fixed a lens, the other end being closed by a plate in which there is a vertical slit, which can be widened or narrowed as required by means of a small screw
The tube E has also on the end nearest the prism a lens, and at the other end a reduced photographic millimetre scale which can be seen through the telescope T
PREPARATION OF SOLUTION FOR BASES
1. Boil the finely-divided substance in distilled water. 2. If insoluble, add ¼ its bulk of strong HCl and boil for two or three minutes. 3. If still insoluble, treat a fresh portion with strong HCl and boil for five minutes ; then add an equal volume of water and warm. The majority of substances will dissolve with the above treatment. 4. If there is still an insoluble residue, decant off the solution from (3), add a little fresh HCl, boil, then add strong HNO3, drop by drop, as long as the substance appears to dissolve
Note 1. Do not boil with Na2CO3 unless necessary. If only alkalies are present it is unnecessary.
Note 2. If organic acids and Groups I. and II. or H2CrO4 are present add HCl, and pass H2S before boiling with Na2CO3 to make solution (4).
The following should be tested for separately:—
HNO3.—Black ring test, with solution of FeSO4 and H2SO4 H3BO3.— To a little of the substance in a watch-glass add strong H2SO4, then C2H5OH; apply a light. If alcohol burns with a green-edged flame = H3BO3. HF.—Sand and H2SO4 test.
TABLE FOR ANALYSIS OF INSOLUBLE SUBSTANCES
The insoluble residue remaining after treating with acids should
Take a few crystals of potassium chlorate (KClO3), place them in a clean dry test-tube, and heat them gently over a small bunsen flame; the salt begins to split, then fuses. Insert into the test-tube a splint of wood, glowing at the point, but do not allow the wood to quite touch the fused salt. The splint, which only glowed when introduced into the tube, bursts into a bright flame with a slight explosion. Withdraw the splint, blow out the flame, and again insert the glowing end into the tube ; the same result follows.
KClO3 (heated) = KCl + O3
The above equation explains what takes place
Before starting to work at Practical Chemistry it is necessary that the student should have some knowledge of how to cut, bend, draw down, and round off the ends of glass tubing, make closed and bulbed tubes, mend test- tubes, top and bottom, and fit up a decent wash-bottle. In this chapter is included also the graduating of test-tubes and beakers, so that the student from the beginning can work economically with regard to the use of reagents.
Cutting Glass Tubes
To cut a glass tube the simplest method is to make a sharp scratch on one side of it with a three-edged file where it is desired to cut, then take the
From very early times the ancients were attracted by the beautiful colour, the brilliant lustre, and the indestructibility of gold, and spared no pains in the endeavour to acquire it. In the code of Menes, who reigned in Egypt in 3600 B.C. or about 2000 years before Moses, the ratio of value between gold and silver is mentioned, one part of gold being declared equal in value to two and a half parts of silver, and it is, therefore, clear that the extraction of both metals from the deposits containing them must have been carried on before that time. It is, indeed, probable that gold was the first