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Previous Next The best candle and soap tips online! to he considered as spoiled. If it is brought in contact with the air it again assumes a blue color. TINCTURE OF COCHINEAL. According to Lucknow, who "vras the first to recommend this tincture as an indicator, 3 grms. (0.11 oz.) of the best cochineal are ground and transfused with a mixture of 50 cubic centimeti'es (1.69 fi. oz.) of alcohol and 200 cubic centimetres (6.76 fl. ozs.) of distilled water, then left to digest several hours, and finally filtered through lime-free paper. This tincture has a dark orange-red color, with L tinge of brown (dark chestnut-red). 10 culnc centimetres (0.338 fl. oz.) of water to 10 drops of the tincture produce a light orange-red fluid. The phenomena during neutralization are, in the case of tincture of cochineal, different from those of the litmus, which, from the beginning, according to the quantity of the tincture employed, turns into purple-violet or in this shade of lighter tinge, then gradually becoming carmine-violet or cherry-red, until the close of the operation. A more or less orange shade appears, when the tincture of cochineal is used. THE BASIS OP ALKALIMETRY For this various substances have been proposed. What substances are used, whether acids or alkalies, is tolerably unimportant, if they can be obtained in their purest state and be weighed oft' with all possible accuracy. Gay-Lussac used the anhydrous carbonate of soda as a base, and neutralized it with sulphuric acid. If the necessary care is observed, the most perfect and ample results for technical purposes are reached by using the carbonate of soda. The great tendency of freah calcined carbonate of soda to absorb moisture caused Mohr to substitute for it crystallized oxalic acid. Although oxalic acid combines ni.my properties which recommend it as a titrimetric substance, and is easily prepared \i a pure Btate, and can also be weighed accurately, ite application as 180 TECHNICAL TREATISE ON SOAP AND CASTLES. ALKALIMETRY. 181 such is nevertheless not without critical objections, since it often contains more water thun corresponds with the formula Cs03 4- HO, and moreover is often not free from small quantities of oxalate of potash and lime. These reasons caused Piiicus to apply the pure carbonate of lime as a basis for alkalimetry, and the suitableness of this selection has been almost everywhere acknowledged. Pure car'jonaie of lime is obtained beat in this way: A certain quantity of nitrate of ammonia is dissolved in ten times as much water, and digested with an overplus of hydrate of lime, by frequent shaking, for several hours, then filtered, and precipitated either with carbonate of ammonia or by leading into it a stream of carbonic acid gas until all the lime combines with the carbonic acid and is precipitated. By evaporating the liquid, the nitrate of ammjuia is reob-tained, which, in this manner, can again be used for producing the pure carbonate of lime. The precipitate is placed upon a filter, washed with distilled water, dried, gently calcined, and preserved in a well-closed glass phial, with the inscription "Pure carbonate of lime suitable for alkalimetry." By means of the carbonate of lime thus obtained, the normal acid is prepared. Nitric acid is to be recommended for this purpose, because it forms with most bases soluble salts. Carbonate of lime consists of:— 1 equivalent oflime = 32 I " of cirlwnic acid = 23 and lias the equivalent Nitric acid consists of— 1 equivalent of nitrogen = 14 5 L1 of oxygen = 40 and lience has the equivalent The normal nitric acid applied in alkalimetry must contain in the litre 54 grammes (1 9 oz), or exactly so much anhydrous acid, that with 50 grammes (1 75 oz.) of carbonate of lime it will be neutralized. The preparing of each an acid is performed thus: Take a pure nitric acid, diluted with water, of a strength to suit, smcl liquid of ammonia, so fixed that equal volumes of acid and of ammonia are accurately saturated. Now weigh accurately 2 grammes of pure carbonate of lime, place the same in A litre flask, pour about 100 cubic centiriie-tres (3.38 fl. ozs.) of distilled water and a suffioieiit quantity of tincture of litmus or tincture of cochineal ou to it, and also add an accurately measured quantity of the acid corresponding with the ammonia, so that all the lime is dissolved and the liquid remains plainly < f red color. The liquid is then heated to boiling, in order to entirely remove the carbonic acid. After this is done and the whole is somewhat cooled oft", the surplus of the acid i? removed by an equivalent of ammonia, and we thus learn, by deducting the cubic centimetre of ammonia used from the applied cubic centimetres ot* the acid, exactly the quantity of acid which has been neutralized by the above-mentioned carbonate of lime. Since the acid must now have such a strength that 1000 cubic centimetres (33.8 fl. ozs.) thereof are neutralized by 50 grammes (1.75 oz.) of carbonate of lime; for 2 grammes of carbonate of lime 40 cubic centimetres (1.36 fl. oz.) of acid must result. If now less acid has been used, as is always the case, the acid must be thus much diluted that 40 cubic centimetres (1,36 fl. oz.) of liquid, that is, normal nitric acid, are produced, and according to this proportion the total (juantity of the equivalent of nitric acid must be diluted to correspond to the ammonia. Supposing we have 750 cubic centimetres (25.4 fl. oz.) nitric acid, its equivalent of ammonia, and of this 2 grammes (30.86 grs.) carbonate of lime, 30 cubic centimetres (1 02 tl. oz.) applied, then those 750 cubic centimetres (25.4 fl. ozs) must be diluted to 1000 cubic centimetres (33.8 il. ozs.), an operation which ia to be performed in the mixing cylinders or in the mixing flask. Inasmuch as 1000 cubic centimetres of this acid con rain 1 equivalent of nitrie acid, they also neutralize each 1 equivalent of any base, respectively alkali or the quantity of a combined acid, in which 1 equivalent of a base is contained, or thev will neutralize:— 182 Previous Next
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