_Carbonate of Potash (Pearl Ash)._--The total or available alkali may be estimated by taking 6.9 grammes of the sample, and titrating with N/1 acid directly, or adding 100 c.c. N/1 sulphuric acid, boiling for a few minutes, and titrating the excess of acid with N/1 caustic soda solution, using litmus as indicator. In this case each c.c. N/1 acid required, is equivalent, in the absence of Na_{2}CO_{3}, to 1 per cent. K_{2}CO_{3}. Carbonate of potash may be further examined for the following:-- _Moisture._--From 2-3 grammes are heated for thirty minutes in a crucible over a gas flame, and weighed when cold, the loss in weight representing the moisture. _Insoluble residue_, remaining after solution in water, filtering and well washing. _Potassium_ may be determined by precipitation as potassium platino-chloride thus:--Dissolve 0.5 gramme in a small quantity (say 10 c.c.) of water, and carefully acidulate with hydrochloric acid, evaporate the resultant liquor to dryness in a tared platinum basin, and heat the residue gradually to dull redness. Cool in a desicator, weigh, and express the result as "mixed chlorides," _i.e._ chlorides of soda and potash. To the mixed chlorides add 10 c.c. water, and platinic chloride in excess (the quantity may be three times the amount of the mixed chlorides) and evaporate nearly to dryness; add 15 c.c. alcohol and allow to stand three hours covered with a watch-glass, giving the dish a gentle rotatory movement occasionally. The clear liquid is decanted through a tared filter, and the precipitate well washed with alcohol by decantation, and finally transferred to the filter, dried and weighed. From the weight of potassium platino-chloride, K_{2}PtCl_{6}, is calculated the amount of potassium oxide K_{2}O by the use of the factor 94/488.2 or 0.19254. _Chlorides_, determined with N/10 silver nitrate solution, and calculated to KCl. _Sulphates_, estimated as barium sulphate, and calculated to K_{2}SO_{4}. _Sodium Carbonate_, found by deducting the K_{2}CO_{3} corresponding to the actual potassium as determined above, from the total alkali. _Iron_, precipitated with excess of ammonia, filtered, ignited, and weighed as Fe_{2}O_{3}. SODIUM CHLORIDE (COMMON SALT). This should be examined for the following:-- _Actual Chloride_, either titrated with N/10 silver nitrate solution, using neutral potassium chromate solution as indicator, or, preferably, estimated gravimetrically as silver chloride by precipitation with silver nitrate solution, the precipitate transferred to a tared filter paper, washed, dried and weighed. _Insoluble matter_, remaining on dissolving 5 grammes in water, and filtering. This is washed, dried, ignited and weighed. _Moisture._--5 grammes are weighed into a platinum crucible, and heat gently applied. The temperature is gradually increased to a dull red heat, which is maintained for a few minutes, the dish cooled in a desicator, and weighed.