ON SOME N.S.W. TAN-SUBSTANCES. 95 



2. I have doubts as to the value of Ammonium sulphide as a 

 Te-agent for tans, and may reject it in future experiments. In 

 addition, Manganese acetate, Chrome alum, Mercuric chloride, 

 and Potassium ferro-cyanide give, in most cases, but poor reactions, 

 while Tartar Emetic and Ammonio nitro-molybdate are not much 

 better. Still, as most of these re-agents have been suggested by 

 various authorities, I have up to the present followed suit. 



3. The other re-agents yield precipitates more or less readily, 

 many of which are characteristic. 



4. I look upon the colour-reaction given by a drop of strong 

 sulphuric acid (Column 10) as the most valuable, for practical 

 purposes, of all. By the colours obtained affinities are indicated, 

 and thus a rough classification of tans is at once feasible. The 

 rich wattle-barks give rose-madder colours, and all give shades of 

 colour proportionate in depth of tint (caused by quantity of colour) 

 to the percentage of tannin. I showed the tile on which these 

 colour reactions had been performed, to an assistant who had not 

 been engaged with me upon tans, and who was perfectly ignorant 

 of the percentages of tannin I had found in the species of Acacia 

 referred to in this paper. Nevertheless, with but one slight 

 mistake, he at once arranged the eight Acacia colours in the same 

 order of tannin-yield, which by gravimetric processes I had proved 

 them to occupy. I cannot but think that we have here a simple 

 and excellent comparative method for the practical tanner. 



5. The tans now under examination range themselves in three 

 groups — a. Acacia vestita, dealbata, binervata, (the two former are 

 very closely allied) b. A. pendula, glaucescens. c. Eucalyptus 

 hcemasto ma, macrorrlvynclia. 



6. The reactions yielded by Acacia colletioides are more or less 

 unsatisfactory, owing to the exceptional poverty of the bark. 



7. The extract of Acacia rigens contains a little mucilage, and 

 to this circumstance, doubtless, some of the abnormal reactions of 

 this species are owing. 



8. The two varieties of Eucalyptus Gunnii bark show a marked 

 difference in their behaviour with dilute ferric chloride. 



9. Precipitates sometimes only form on standing. It is therefore 

 necessary to allow a period of not less than two hours to elapse 

 before completing the examination of a precipitate. In all cases, 

 it is to be assumed that there is no change on standing, unless the 

 contrary is stated. 



10. The colour reactions have been given with much care and 

 detail, as the description of these organic precipitates is frequently 

 not unattended with difficulty. 



