52 REPORT OP THE COMMISSIONER OP AGRICULTURE. 



ia Hungary, is variable, two samples analyzed containing respectively 

 0.98, 0.84, knd 0.70 per cent, nitrogen, and 11.03 and 10.56 per cent, 

 pliospboric acid. A sample from an Italian deposit, analyzed by F. 

 Sestini,* contained 20.799 per cent, volatile matter, (principally organic,) 

 2.021 per cent, nitrogen, and 1.17 per cent, phosphoric acid. With these 

 facts before us wo may readily recognize the importance of the develop- 

 ment of these deposits in the South, where fertilizing materials are so 

 much needed and are so costly, and especially is this true when, they 

 may bo obtained from, this source for the mere cost of removal. 



AMERICAN TANNING MATERIALS. 



Under this head, I propose to submit the results of the analyses of the 

 vegetable substances containing sufficient of tannic acid to make them 

 of value for tanning that were collected and prepared for exhibition in 

 the late International Exhibition in Philadelphia. The list may not 

 comioriso all the indigenous products that are of value in this respect, 

 but some of them, at least, have not yet received extended application. 



The methods laid down for estimation are numerous, but nearly all of 

 them are liable so many objections as to render their results extremely 

 unsatisfactory, and, in fact, this condition is destined to continue until 

 we have more definite knowledge of the constitution of the varieties of 

 tannic acid found in different plants. In previous estimations we have 

 proceeded by extraction with ether, exhausting the residue obtained from 

 the etheral extract by distillation with water, and determining the 

 amount of tannic acid in the aqueous extract by titrating with a stand- 

 ard solution of potassic permanganate after the addition of a known quan- 

 tity of potassic sulphindylate. In the estimations in which the present 

 results were obtained this method was abandoned, on account of the 

 difficulty of complete extraction of the tannic acid by means of the ether, 

 too much time being required, and we adopted the method lately de- 

 scribed by F. Jean, in the Bulletin de la Soci6t6 Chimique de Paris, 

 XXV, 511, which depends upon the absorption of iodine by tannic acid 

 in presence of an alkaline carbonate. It consists in titration of the 

 solution containing tannic acid with a standard solution of iodine in 

 potassium iodide, the end of the reaction being determined by placing 

 a drop of the solution under titration on a white paper covered with 

 starch. While this method is open to some objections, one of which is 

 the troublesome character of the end reaction, wo consider it on many 

 accounts the most satisfactory that has yet been devised. By this method 

 the proportion of tannic acid foun.d in the various samples respectively 

 is as follows : 



Per cent. 



Gronnd sumac, (mixed,) from Winchester, Va 24. 18 



Sumac, (lihus cotinus,) Hallsborougb, Va..... 24.08 



Sumac, (Ilkus glabra,) Georgetowu, D. C 2(). 1 



Leaves of sweet fern, (Cornptonia asplenifolia,) from near Boston, Mass U. 42 



Leaves of Polygonum amphibiiim, from Nebraska 11. G 



Ephedra antisyiihilitica, from the table-lands of Arizona and Utali 11. 1) 



Bark of sweet-gum, {lAqnidamhar styracijlua,) from District of Coluinbia 8. 'AG 



Bark of red oak, (Qticrcus rubra,) from Canton, 111 ;">. 55 



Bark of white oak, (()«c)T(/8 a/&a,) from Canton, 111 7.35 



Crushed quercitron bark, (Qucrcus nigra,) from Winchester, Va (J. 47 



Bark of Quercus coccinea, from Canton, 111.... 7.78 



Bark of Qucrcus macrocarpa, from Canton, 111 7. 85 



Bai:k of hemlock, {Abic8 canadensis,) Van Etteuvillo, N. Y 9.5 



*Landw. Vertiacha-Stationen, xix, 10. 



