----------------------+------------------------------------------- | Antiseptics. | Solution after Five Months. ----------------------+------------------------------------------- | Menthol in KOH..... | Some growth at bottom, upper layer clear. | Thymol in KOH..... | Growth at top, gum white and opaque. | Salol in KOH........ | Growth at top, gum black and opaque | Saccharin in KOH ... | White growth at top. | Boric acid............| Remained clear; did not smell. | Sodium phosphate ... | Slight growth at top. | Potash alum......... | Slight growth at top. ----------------------+------------------------------------------- The solution to which no antiseptic had been added was of course quite putrid, and gave the reactions for acetic acid. In the earlier part of this paper we have given a short account of the chief characteristics of the more important gum substitutes. The following additional notes may be of interest. The ashes of most gum substitutes, consisting chiefly of dextrin, are characterized by the high percentage of chlorides they contain, due no doubt to the use of hydrochloric acid in their preparation. The soluble constituents of the ash consist of neutral alkaline salts, but as a rule no alkaline carbonates, and it is thus possible to demonstrate the absence of any natural gum in such a compound. We have seldom noticed the presence of any sulphates in such ashes, but when sulphurous or sulphuric acids have been used in the starch conversion it will be found in small quantities. We have already pointed out that the potash absorption value of a gum is low and that dextrins give high numbers, but the latter vary very considerably, and as the starch and sugar present also influence the potash absorption value, it does not give information of much service. The following table shows the kind of results obtained: -----------------------------+----------+--------------+-------------- Sample. | KOH | Starch. | Real Gum. | absorbed.| | -----------------------------+----------+--------------+-------------- | | Per Cent. | Per Cent. Dextrin, 1 | 25.40 | 1.99 | .. Dextrin, 2 | 19.70 | 13.13 | .. Dextrin, 3 | 7.57 | 24.72 | .. Artificial gum, 1 | 19.70 | 10.98 | 9.00 Artificial gum, 2 | 13.70 | 8.05 | 23.50 Starch | 9.43 | 100.00 | None -----------------------------+----------+--------------+-------------- The baryta absorptions seem to be chiefly due to the quantity of starch present in the composition: