THE SKIN AND HAIR. 85 



less ; calling up reminiscences of a grandmamma's black-silk 

 dress treasured from her girlhood; or a black-silk dress of 

 more modern origin that has come across the sea on the back 

 of a deck-passenger. 



Lead is not the only metal that has this function of 

 turning black when dissolved and brought into contact with 

 sulphuretted hydrogen. Bismuth preparations are affected 

 with a similar change, though the tint of blackness slightly 

 differs. Gold is in the same category, and indeed most of the 

 ordinary metals. Four, however, are exceptional, and one of 

 them is iron ; yet the belief that iron actually imparts dark 

 colouring-matter to certain tints of hair as a natural con- 

 stituent has suggested the use of iron-salts in the process of 

 artificial dyeing. They can be so used, but not alone. Some 

 second solution must be employed by way of mordant to 

 develop and fix the colour. The Turks use pyrogallic acid to 

 this end, as I have already announced ; common gallic acid 

 would not yield black of such unimpeachable colour. British 

 and other west European hair-dyers, when they avail them- 

 selves of iron solutions for dyeing hair, employ usually neither 

 gallic nor pyrogallic acid. They use for this purpose a solu- 

 tion of hydrosulphate of ammonia, which will blacken iron 

 solutions, though uncombined hydrosulphuric acid will not. 

 I am not aware that iron dye thus mordanted is used for any 

 more extensive purpose than for the dyeing of whiskers and 

 moustaches, or, at the most, beards. The abominable odour 

 of hydrosulphate of ammonia compounded of the smell of 

 putrid eggs with hartshorn would, I should think, make the 

 application of this sort of dye to a full head of hair intoler- 

 able ; and a fellow who could complacently apply this hateful 

 thing to his moustache must be strong of stomach, and not 

 over delicate as to the sense of smell. 



To all hair-dyes one general remark applies, and it is 

 the following : if the illusion of the change of colour effected 

 by them is to last, the dyeing must be gone through con- 



