266 ON SOME N.S.W. TAN-SUBSTANCES. 



In the example now given N - V = 8.4 (W) that is to say, the 

 amount of permanganate required to oxidise the matter absorbable 

 by hide powder. 



In the sample taken the moisture was ascertained to be 

 10*4 per cent. ; this would bring W up to 9-375. 



Now according to Schroeder (Procter, op. cit., 129) " With 



the purest samples of tannin the permanganate value estimated 

 on the total dry substance of the tannin varied by very little 

 from that of the part of the tannin absorbed by a piece of hide, 

 but on the average bore the proportion of 1:1 -05." Therefore, 

 multiplying 9*375 by 1*05 we have the true permanganate value 

 of Schering's tannic acid. 



Speaking of the tannic acid taken for standardisation purposes : 

 " If the non-tannin does not exceed 5 per cent, of the total, it is 

 good, but it may be used so long as the non-tannin does not 

 exceed 10 per cent." (Procter.)* In the present instance 45 (V) 

 is 5*085 per cent, of 8*85 (N), and thus while slightly below the 

 standard of "good," comes well within the category of "may 

 be used." 



We now are in a position to understand how results are 

 obtained with the typical example (Acacia scdicina). 



The principal objection to the use of Lowenthal's process is 

 that a percentage of gallic acid is absorbed by hide powder as 

 well as the whole of the tannic acid. But inasmuch as that 

 percentage is very small in most tan-substances, it has been the 

 invariable practice to neglect it. What is the percentage of 

 gallic acid in the New South Wales tan-substances I have 

 operated upon, must be left for a separate investigation. 



79. Cupania semiglauca, F. v. M., N.O. Sapindacese, B. Fl., i., 

 457. 



Found in New South Wales and Queensland. 



Sample obtained from Bangley Creek, Cambewarra. Height of 

 tree 20 to 30 feet, diameter 8 to 12 inches. Collected 17th May, 

 1888. Analysed 20th to 22nd August, 1888. 



Externally this bark might perhaps be mistaken by an expert 

 for Black Wattle bark (A. decurrens). Certainly it would 

 require more than a casual observation to detect its substitution 

 if admixed with Wattle bark in the bundles as ordinarily sent to 

 market. But on close examination the following differences 



*A later statement of Procter's is in these terms, "If the 



permanganate it consumes is less than 10 per cent, of the total consumed 

 by the tannin, it may be taken as being one of the best of commercial 

 preparations, and suitable for the purpose in view." The italics are mine. 



