=Testing Stick.=--Stick is tested the same as tank water, excepting a hydrometer graduated from 20° to 40° is used. It is usual to evaporate to a density of 29° Beaume, which is 64.61 per cent dry solid. To calculate the quantity of concentrated or dry stick containing 4 per cent moisture produced from 29° Beaume stick, multiply the number of gallons of stick by 10.27 lbs. to get weight of 29° Beaume stick; then take 64.61 per cent of this weight, which is weight of dry solids, then add 4 per cent moisture to this amount by dividing the weight of dry solids by .96; the result is weight of concentrated tankage containing 4 per cent moisture. =Copperas.=--This is usually “sulphate of iron” of commerce, although some institutions make their supply thus: Using a lead-lined vat holding about 200 gallons; into this put about 160 gallons of 60-degree sulphuric acid, adding water enough to make the solution about 12° Beaume. Into this solution place scrap iron of any description and allow it to stand until the solution will dissolve no more iron. Pump the solution into a shallow lead-lined vat with lead coils, and evaporate to about 40° degrees Beaume. It is next drawn off into barrels of fifty gallons each and to each barrel add forty pounds of black oxide of manganese and thoroughly mix. =Copperas in Water to Evaporate.=--An early practice and one which had the merit of fixing free ammonia before it passes off in a gaseous form was the introduction of copperas in tank water, while settling, and before evaporation. The vats of tank water are tested with a Beaume hydrometer and for every 2,000 gallons of tank water at indicated degree, Beaume, ordinary commercial copperas should be added as follows: Water testing 5° Baume 166 lbs. dry copperas Water testing 4¹⁄₂° Baume 150 lbs. dry copperas Water testing 4° Baume 133 lbs. dry copperas Water testing 3¹⁄₂° Baume 117 lbs. dry copperas Water testing 3° Baume 100 lbs. dry copperas These varying amounts of copperas are put into a barrel of hot water and thoroughly stirred until dissolved. The solution is then poured into a vat of tank water, the mass allowed to stand six or eight hours, and then skimmed off before being pumped to the evaporating machine. =Solids in Water.=--The percentage of solids and liquids, as well as the respective weights in tank water at different degrees Beaume, are shown in the following table: TABLE FOR TANK WATER.