THE ANALYST. 179 THE RAPID ESTIMATION OF BORIC ACID I N BUTTER. BY H. DROOP RICHMOND, F.I.C., AND J. B. P. HARRISON, F.I.C. (Read at the Meeting, April 9, 1902.) THE report of the Preservatives Committee recommending a limit of 0.5 per cent. of boric acid in butter has rendered it desirable to make the estimation of this substance as simple and rapid as possible. We have been in the habit of using a slight modification of Thomson’s method : About 25 grammes of butter is weighed into a stoppered cylinder, enough water to make with the water already present a number of C.C. equal to the weight of butter in grammes, and 10 to 15 C.C. of chloroform are added ; the contents of the cylinder are warmed, mixed, and allowed to separate ; an aliquot portion of the aqueous solution is drawn off (each C.C.containing the boric acid of 1 gramme of butter), made alkaline, evaporated, ignited, and the soluble ash dissolved in hot water. This solution is made neutral to methyl orange, boiled to expel CO,, and, after the addition of glycerol, titrated with standard alkali. We have proved the accuracy of this method, have found that the insoluble ash is free from boric acid, and have also ascertained that the ignition cannot be dispensed with, the results without it being from 0.05 to 0.10 per cent. too high. The evaporation, ignition, and extraction of the ash with hot water take up some little time, and we experimented to find a method which would avoid this. Our first experiments were with a slight modification of Deniges’ method for the estimation of boric acid in milk (J.Pharm. Chim., vi. (2), 49), but we failed to obtain sufficiently concordant results, due, as we soon found, to the fact that the end-point, when titrating boric acid with phenolphthalein in milk-sugar solution, varied greatly with the temperature. We found, however, that when the solution was boiling the end- point was constant and sufficiently sharp. The end reaction is distinctly sharper in180 THE ANALYST. milk-sugar solution than in water ; a 5 per cent. solution of milk-sugar was some- what arbitrarily adopted. Our preliminary experiments were made with a weighed quantity of boric acid dissolved in 10 C.C. of water, to which was added 15 C.C. of a 10 per cent. milk-sugar solution and 3.25 C.C. of water (the average amount contained in 25 grammes of butter).A few drops of phenolphthalein were added, and the solution raised to the boiling-point ; caustic soda solution was added till a faint but distinct pink colour was observed ; about 15 C.C. of glycerol was then added, and the solution titrated until a pink colour was produced. The following results were obtained : Boric Acid found. taken. Milk-sugar Solution. Glycerol Solution. 0.100 0.53 3.23 2-70 0.099 0.070 0.33 2-24 1.91 0.070 0.050 0.26 1.62 1.36 0.050 0.020 0.10 0.65 0.55 0.020 Difference. Boric Acid C.C. of 4 Soda in C.C. $ Soda in It is seen that the difference between the two titrations indicates 84.4 per cent. of the total boric acid, and 1 C.C. of soda is equal to 0.0368 grammes of boric acid. The influence of slight dilution was studied ; a 1 per cent.boric acid solution was used. Ten C.C. boric acid solution+15 C.C. 10 per cent. milk-sugar solution+O C.C. water, indicated 0.100 gramme boric acid. Ten C.C. boric acid solution + 15 C.C. 10 per cent. milk-sugar solution + 3.25 C.C. water indicated 0.100 gramme boric acid. Ten C.C. boric acid solution + 15 C.C. 10 per cent. milk-sugar solution + 7.5 C.C. water indicated 0.098 gramme boric acid. The dilution due to the extreme percentages of water likely to be met with in butter will not affect the determination. Various substances which may occur in butter were added to the boric acid solution. Ten C.C. boric acid solution + 15 C.C. 10 per cent. milk-sugar solution + 4 C.C. milk indicated 0.100 gramme boric acid. Ten C.C. boric acid solution + 15 C.C. 10 per cent.milk-sugar solution + 3.25 C.C. of a solution containing butyric and caproic acids indicated 0.100 gramme boric acid. Ten C.C. boric acid solution + 15 C.S. 10 per cent. milk-sugar solution + 3-25 C.C. of a solution containing 0.030 gramme P,O, indicated 0.102 gramme boric acid. Ten C.C. boric acid solution + 15 C.C. 10 per cent. milk-sugar solution + 3-25 C.C. of a solution containing 0.059 gramme P,O, indicated 0.102 gramme boric acid. It is thus seen that none of the substances likely to be present in butter will affect the determination. Considerable quantities of phosphoric acid have, however, a prejudicial effect; a solution free from boric mid, and containing 0.297 gramme P,O,, indicated 0.019 gramme of boric acid.BlIixtures of boric acid and borax may be titrated by adding a, littie mineral acid t o liberate boric acid from the borax.THE ANALYST. 181 An amount of commercial preservative equal to 0.100 gramme of boric acid indicated 0.103 gramme boric acid. As the result of our experiments, we have adopted the following method: Weigh out 25 grammes of butter in a beaker, add 25 C.C. of a solution containing G grammes of milk-sugar and 4 C.C. N sulphuric acid to 100 C.C. Place in the water- oven till the fat is just melted and stir well; allow the aqueous portion to settle for a few minutes and draw off 20 C.C. ; add a few drops of phenolphthalein, bring to the boil, and titrate with soda till a faint pink colour just appears ; add 12 C.C. glycerol, and titrate till a pink colour appears.The difference between the two titra~ons, less the amount of alkali required by 12 C.C. of glycerol, multiplied by 0.0368, will give the amount of boric acid in 20 c.c., and this, multiplied by 100 + percentage of water 20 ~ ~- _ _ _ - will give the percentage, If the percentage of water is about the average, it may be taken as 13 without appreciable error. Generally, the number of C.C. of soda used, multiplied by 0.2, will very closely approximate to the percentage of boric acid. The following test experiments will show that the method is accurate enough for all purposes. They were made by weighing out 25 grammes of butter free from boric acid, adding a known weight of boric acid or a commercial preservative of known boric acid value, and estimating as already described : Boric Acid added. Per Cent.0.10 .. ... 0.25 ... ... 0.35 ... ... 0.45 ... ... 0-56 ... ... 0.62 ... -.. 0.88 ... ... Boric Acid found. C.C. Soda Per Cent. -!- 0.2 ... 0.11 .. ... ... 0.11 ... 0.26 ... . _ _ ._. 0.25 ... 0.36 .. ... 0.35 ... 0.46 ... ... ... 0-44 ... 0.55 ... ... ... 0.52 ... 0 60 .. '.. ... 0.58 ... 0.86 ... ... ... 0.84 Butters free from boric acid have shown a difference between the two titrations equal to the amount of alkali required by the glycerol. We communicated the method to Mr. Hehner, and at his request Ur. B. W. J. Warren has sent the following results to us : Boric Acid added. Boric Acid found. Per Cent. Per Cent, 0.48 ... ... ... ... ... 0.50 0.60 ... ... ... ... ... 0.59 0.67 ... ... ... ... ... 0.70 0.47 .. ... ... ... . . 0.46 0.11 ... ... ... ... 0.13 Mr. Warren also found in another butter 0.45 per cent. in daylight, and 0.44 and 0.42 per cent. by gaslight.182 THE ANALYST. DISCUSSION. Mr. B. W. J. WARREN said that one difficulty he had met with in his experiments referred to in the paper was the production of a pink colour, which rendered one very liable to overshoot the mark in titrating. He had found, however, from some investigations of Mr. R. T. Thomson, that lacmoid would answer a similar purpose to methyl orange, and he had accordingly experimented with lacmoid, and had obtained very good results. The lacmoid could be easily seen in the turbid solution obtained from the butter. Mr. F. J. LLOYD inquired why a solution of milk-sugar was used.He had made estimations simply by extracting with boiling water and filtering, and had found no difficulty in obtaining accurate results without using a solution of milk-sugar-simply adding the sulphuric acid and boiling. Mr. RICHMOND hoped that the very interesting information which Mr. Warren had given with regard to the use of lacmoid, which was certainly more convenient to use than phenolphthalein, would be embodied not merely in a short note in this discussion, but in a paper before the Society, going more fully into the details of the method, and giving the results obtained. Mr. Warren’s method appeared, as far as he could see, to be better than their own, and he should try it at once. Before answering Mr. Lloyd’s question, he would like to hear exactly how Mr.Lloyd obtained the result he mentioned with water-whether he titrated, first of all, with methyl orange and then with phenolphthalein and glycerol, or simply, as they had, first titrating, till the pink colour appeared, with water, then adding glycerol, and going on with the titration and taking the difference. Mr. LLOYD said that the titration was made first with methyl orange, and then with phenolphthalein and glycerol, methyl orange being used before the addition of the glycerol. Mr. RICHMOND said that in that case he could hardly understand Mr. Lloyd getting accurate results, because there must be a certain amount of casein and other proteids in the aqueous portion, as well as a certain amount of phosphoric acid in the form of phosphates. These two both interfered when methyl orange and phenol- pbthalein were both used, because the end-points for methyl orange and for phenol- phthalein were very different. That was the reason for stating in the paper that evaporation and ignition could not be dispensed with, the results otherwise being from 0.05 to 0.1 per cent. too high. The reason for using milk-sugar was that they had found that with milk-sugar, in boiling solution, the end-point was sharper than was the case in an aqueous solution simply. The true reason was that the amount of dissociation was more sharply determined in the milk-sugar solution than in the aqueous solution, the practical result being that the end-point was easier to see.