1883.] NATURAL SCIENCES OF PHILADELPHIA. 299 



cloudy and deposit large quantities of an insoluble sediment. It 

 therefore can be readily understood that an extract of logwood, 

 prepared by the evaporation of an infusion of the drug, must be to 

 some extert changed by the process of manufacture, and that any 

 preparation made from it would (the process of decomposition 

 having alreadj' been started) become much more liable to change. 

 And just such a result takes place in staining fluids prepared from 

 extract of logwood. The partially oxidized tannin in the liquid 

 graduall}^ absorbs more oxygen from the air, and changes to other 

 complex organic compounds ; the coloring matter is also affected 

 by the decomposition, and gradually becomes converted into 

 other substances, and the liquid finally becomes of a dirty, muddy 

 color, and is half filled with a lump}' sediment. This change will 

 be found to take place in all ordinary' logwood staining fluids, 

 whether prepared from the extract or from the drug itself, although 

 from the nature of the case those made from the extract would lie 

 the most quickly affected. The idea, therefore, occurred to my 

 mind, that if the tannin could be removed, and the lake of log- 

 wood isolated in a state of comparative purity, a staining fluid 

 could be prepared whicii might possibly be both permanent and 

 satisfactor}-. After numerous and lengthy experiments, the 

 desired ol'ject was obtained, and the formula which I now present 

 to your notice is the result of my investigation on the sul)ject. 

 As a means of distinguishing this preparation from the other and 

 generally worthless logwood fluids, I have thought it best to call if 



'' Mitchell's Hematin Staining Fluid." 

 R 



Finely ground logwood, . . , . , . 3 ij. 



Sulph. aluminum and potash (potash alum), . . . 3 ix. 



Glycerine, . . . . . . . . /. S iv. 



'Distilled water, .... a sufiicient quantity. 



Moisten the ground logwood with suflflcient cold water to slightly 

 dampen it, place it in a funnel or percolator, packing it loosely, 

 and" then percolate sufficient water through the drug until the 

 liquid coming from the percolator is but slightly colored. Allow 

 the drug to drain thoroughly', and then remove it from the perco- 

 lator, and spread out on a paper or board to dr}'. Dissolve the alum 

 in eight fluid-ounces of water, moisten the dr}' drug with a suffi- 

 cient quantity of the fluid, and again pack in the percolator, this 

 time rather tightly, and pour on the remainder of tlie alum solu- 



