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



sufficient detail (I am speaking of a research, or an analysis as 

 accurate as possible, and not of a merely approximate determination 

 of tannic acid) for every purpose of the student. To my mind 

 the process is best described by Mr. Henry R. Procter, one of 

 the foremost of English tanning chemists, in his Text-book of 

 Tanning, and also fairly well in an American publication, The 

 Manufacture of Leather (C. T. Davis). But both lack a fully 

 worked out illustration, and even Procter, while taking notice of 

 many of the difficulties of this confessedly difficult subject, omits 

 certain details which my own experience convinces me are worthy 

 and necessary to be recorded. 



I therefore propose to state in detail the process of Lowenthal, 

 and I trust that this will serve the double purpose of hints for its 

 use by Australian chemists, and also of indicating every step by 

 which the results recorded by me in this paper have been obtained. 



To show how necessary a careful and uniform system of working 

 is required with even Lowenthal's process, considered the most 

 perfect process yet introduced, Procter states (Journ. Soc. Chem. 

 Ind. 79, 1886), "that there are certain inherent defects in the 

 method which preclude its ever being of the highest scientific 

 accuracy, and which require strict attention to ensure even the 

 degree of exactness which is needed for technical purposes." 

 Certainly I can state that the process must not be attempted 

 unless the analyst is prepared to devote many preliminary 

 experiments to accustom himself to it, and always to be on his 

 guard. But with perhaps more precautions than are necessary 

 in most methods, I have found it always to give rapid and 

 satisfactory results. 



Materials Employed. 



1. Snlphindigotate of soda. The article I have been using is 

 of German origin, and is labelled " Indigotine 1. (Arsenfrei)." 

 It is of the highest quality, and perfectly uniform. 



'2. Potassium permanganate (chemically pure). 



3. Hide powder. Hide purified, and in a fine state of division,, 

 forming a kind of fluff. Nearly white, but of a creamy tint. 

 This substance is not at present obtainable in the Colony, but 

 when its utility shall have been realized in Australia, an 

 enterprising firm will doubtless supply it in abundance, pure and 

 fresh. 



4. Sulphuric acid (chemically pure). 



5. Tannic acid (Schering's best). 



Standard Solutions. 

 A. Five grammes indigotine, together with fifty grammes 

 sulphuric acid are agitated with one litre of distilled water, 

 allowed to stand a night, and then filtered. The filtering is of 

 the highest importance to secure a homogeneous liquid. 



