REMOVAL OF IRON MOULD. 137 



and the danger of destroying the fabric so as to produce holes, may 

 be diminished, by dropping solution of ammonia (not too strong) 

 on the stain, so that the spot disappears. If the acid spilt be 

 nitric acid, and the spot have turned yellow, this treatment will 

 usually not suffice to bring back the original colour, but it will 

 often prevent a hole being produced, if the ammonia be applied 

 soon enough. 



When clothing becomes faded in colour, the original tint may 

 often be more or less restored by sponging with water to which a 

 little ammonia solution has been added; the fading being due 

 to the acid vapours in the air, perspiration, &c. 



Expt. 140. To remove Ink Marks from Paper. Black 

 ink of the older kind is made from solutions containing iron mixed 

 with materials of the nature of the substances used in tanning 

 leather, such as gall-nuts, &c. (Expt. 294), which bodies give rise to 

 an intensely black compound, especially after the writing has been 

 exposed to the air so as to cause a certain amount of oxidation 

 to take place, which deepens the tint ; some of the modern inks, 

 however, are made of different materials. Writing done with the 

 former kind of ink can be removed from paper, &c., by brushing 

 dilute hydrochloric acid over the marks, and by and by washing 

 them well with water, using a soft camel's-hair brush, and well 

 pressing with blotting-paper to remove all acid which otherwise 

 might rot the paper, and make it brittle and fragile. The acid 

 decomposes the black colouring matter and dissolves the iron, so 

 that water can wash out both the tanning substance and the iron 

 compound, and thus entirely remove the marks. 



Expt. 141. To remove Iron Mould from Linen, &c. If ink be 

 spilt on linen (tablecloths, &c.), the black marks will often become 

 yellowish-brown after washing, thus producing stains of "iron- 

 mould;" contact with rusty iron, &c., may also stain linen 

 similarly. Such stains may be removed by the same means as 

 those above mentioned with respect to ink marks, i.e., cautiously 

 treating with dilute hydrochloric acid, and then well washing to 

 remove the acid. 



Instead of hydrochloric acid, oxalic acid or citric acid may be 

 used, or a sour substance known as acid oxalate of potassium 

 (sometimes called "salts of sorrel"). Lemon juice will often 

 answer the purpose, this fluid containing citric acid. All these 

 preparations have the advantage that they do not rot or injure the 

 fibres as readily as hydrochloric acid might possibly do if used too 

 strong, or allowed to remain on too long. 



Expt. 142. Changes of Colour produced by Acids and Alkalies. 

 Many dye-stuffs now in use are affected by acids and alkalies so 



