OBSERVATIONS OX THE CYANIDE OF ZINC AND MERCURY 325 



irritating to the nostrils, and besides, if it dusted out, the dressing charged with 

 it would lose more and more of its virtues. I described at the Medical Society 

 a means by which this was prevented ; how by the use of starch the powder 

 might be fixed in any fabric which was charged with it. But I have long felt 

 that it would be an exceedingly desirable thing if this material could in some 

 way be coloured, because, being perfectly colourless, if a gauze is charged with 

 it, we have to trust entirely to the manufacturer as to whether the antiseptic 

 element is present in due proportion or is not. It would be very advantageous 

 if it could be coloured, so that we might see by the tint where the antiseptic 

 substance was, and whether it was uniformly distributed or otherwise. Therefore, 

 before publishing the note which I had promised as to the preparation of the 

 substance, I made attempts to stain this material. I tried various forms of 

 dye, and I found that some of the aniline dyes are precipitated by this zinco- 

 mercuric cyanide and some are not. For instance, magenta is not precipitated 

 in the least, but methyl-aniline violet, and gentian violet, which seems to be 

 a mere variety of the same thing — these are precipitated, and an exceedingly 

 small amount of the dye is sufficient to give adequate colour to the double cyanide. 

 I proceeded to charge a piece of gauze with some of this dyed cyanide, to see 

 how it would tint it ; and when it was dry I was much surprised to find that 

 the gauze charged with the tinted cyanide did not dust in anything like the 

 same degree as a gauze would have done which had received the untinted salt ; 

 so much so that a gauze charged with the tinted cyanide was \'ery much on 

 a par as to dusting with the gauze charged by means of starch. 



Of course, if this were so, it would be a ver}?- satisfactory arrangement ; 

 we should dispense with the starch and also with a quantity of sulphate of potash 

 which was used for purposes that I need not here refer to ; ^ we should greatly 

 simplify the method of manufacture, and also, by getting rid of the starch, we 

 should make our gauze softer and more comfortable to the patient. It seems 

 a remarkable thing that the dye should thus be able to fix the powder. Of 

 course, we understand how the starch docs it. The starch particles, becoming 

 attached to the particles of the cyanide, glue them, as it were, to the fibres of 

 the fabric. But how can we explain this dj-e, in the minute quantity in which 

 we use it, answering the same purpose ? I have here some gentian violet dis- 

 solved in 50,000 parts of water, and you see the great colouring power that this 

 dye possesses. If I take a piece of gauze and dip it into the solution up to 

 a certain point, you will see the gauze coloured up to that point, but the part that 

 is moistened above by capillary attraction is colourless, showing the a\'idity 

 with which the fabric seizes the dye. The dye has a remarkable fondness for 



' Sec p. 31S of this voluino. 



