ECONOMIC POSSIBILITIES OF MANGROVE SWAMPS. 59 



duce any brightening effect without the precipitation of large quantities 

 of tannin. Carbon monoxide does not cause loss of tannin, but its 

 bleaching effect is slight and not permanent. The method of Lepetit, 

 very successfully used for "sulphiting" quebracho, destroys some tannin 

 and neither bleaches nor clarifies. Sodium bisulphite was used in this 

 test and the liquor was heated in an autoclave for eight hours at a temper- 

 ature of 11.5° to 120°. Alkaline salts and hydroxides, such as sodium 

 sulphite, borax, ammonia, caustic soda and the like, dissolve the "insolu- 

 bles" readily. As an alkaline liquor can not be used for tanning, these 

 reagents are useless. However, it was found that treatment with a dilute 

 alkali under pressure at 110° to 120° for three to six hours rendered 

 the "reds" quite soluble in acid solution. Neither acetic, lactic, nor 

 sulphurous acid precipitated them even after several hours' standing. 

 Evaporation to dryness once more rendered them insoluble. It is partic- 

 ularly noteworthy that although the tannin of the treated extract was not 

 destroyed by sulphurous acid, as was the case with the untreated 

 material, there was no appreciable brightening of the liquor. Such an 

 extract gives a nearly black leather and is unserviceable for tanning. 



Nascent hydrogen is the best lileaching agent so far found. It is 

 best generated with aluminum shavings and sulphuric acid, as the pres- 

 ence of small quantities of aluminum sulphate is not detrimental to 

 the extract. The aluminum should be in excess so as to leave no acid 

 to attack metal evaporating vessels. If the liquor is extremely dark and 

 .much acid must be added to bleach it, the bulk of the reagents in solu- 

 tion can be removed with baryta water. However, care should be taken 

 that alkalinity is not reached, for the liquor will then darken more 

 rapidly on evaporation and the leather is more likely to be stained by 

 the barium hydroxide present. 



By this method the "reds" are dissolved to a slight extent and the 

 remainder coagulate and settle with the barium sulphate. An extract 

 so treated gives a leather of good color, which darkens comparatively 

 little on exposure to air. 



Patents have recently been taken out for two processes especially de- 

 signed for mangrove extract. One of them by Damkohler u. Schwindt 

 (Eng. Pat. 24899, Oct. 29, 1909), ^^ is based on the action of the 

 "nascent hydroxides of metals" which are generated by electrolysis. A 

 nonelectrolytic process included in the same patent is that of adding 

 barium aluminate to the extract, and afterwards sulphuric acid or sul- 

 phates to clear the liquor. The complete specifications for the patent 

 are not obtainable in Manila so that it was not thought worth while 

 to test the electrolytic method. However, the nonelectrolytic process 

 promises very well from the tests made with it. An extract so treated 

 gave an excellent light-colored leather. 



"Abstracted in Jonrn. Soc. Ghem. Ind. (1910), 29, 365. 



