Iron Mordant. 59 



Iron mordant^ No. 1 .—Dissolve 20 lbs iron alum in 80 lbs 

 of warm water, add 20 lbs sugar of lead, and agitate the 

 mixture until all the sugar of lead is completely dissolved. 

 This mordant when thickened with starch is employed es- 

 pecially for dark rust yellow ; in block printing it gives also 

 with prussiate of potash a clear dark chemical blue. After 

 some days this mordant becomes turbid, and oxide of iron 

 precipitates. It is, therefore, proper not to prepare more 

 than can be used in the course of 1 or 2 days. As the 

 mordant clears quickly, there is no difficulty in forming it 

 on the instant by keeping prepared solutions of 20 lbs iron 

 alum in 40 lbs water, and of 20 lbs sugar of lead in 40 

 lbs water. These can be added to each other when the 

 mordant is required. 



When vinegar is added instead of the water, no change 

 takes place and no oxide of iron is precipitated. Such a 

 mordant answers very well in place of nitrate of iron as an 

 addition in block printing. 



Iron mordant No. 2. — Dissolve 10 lbs of iron alum in 80 

 lbs of warm water, add 10 lbs sugar of lead, and agitate 

 until all the sugar of lead is completely dissolved. 



This mordant is employed for dark colourless grounds; 

 the cloth should be dyed in the manner before discribed, 

 and dried as quickly as possible. This mordant is also subr 

 ject to the same changes as the iron mordant No. 1. It 

 may be preserved by the same means, viz., vinegar adding 

 only half the quantity of water. 



Calico takes up from a solution of oxide of iron and 

 acetic acid mo^e iron than from a sulphuric acid solution, 

 when also the proportion of oxide of iron is equal in both. 



If two solutions are made of 1 lb iron alum in 20 lbs 

 water, and to one of them 1 lb sugar of lead is added, and 

 both be employed as mordants, while two equal pieces of 

 calico are placed in contact with them for \ of an hour, then 

 rinsed and dyed in tannin colours are obtained of different 

 shades. From which it is obvious that the oxide of iron 

 can be taken up in greater proportion from the acetic acid ; 

 solution formed by the addition of sugar of lead, than from 

 the sulphuric acid solution ; it also appears that the acetic 

 acid iron mordant is much more rapidly exhausted of its 

 proportion of iron, and therefore, must always be employed 

 in a weaker state for this purpose. It is, therefore, neces- 



