212 The Art of Dijeing . 



If we mix 4 loths (1-876 oz.) water, with 1 loth (-469 oz.) 

 sulphuric acid, (which must be done by pouring gradually 

 the sulphuric acid into the water, not by pouring the water 

 at once into the sulphuric acid, as with great quantities a 

 heat is produced) ; and, after cooling, place a portion of 

 cotton in the mixture ; the cotton has not lost its firmness 

 in the course of an hour. But, if the saturated cotton is 

 hung up in a warm place, as soon as it begins to dry, it 

 becomes tender and at last falls to pieces like tinder. This 

 also happens when the acid is even more dilute. Hence, it 

 follows, that no dilute sulphuric acid should be allowed to 

 come in contact with cotton, when the latter can become 

 dry, or the water evaporate. Boiling with dilute sulphuric 

 acid is also deleterious. 



On the other hand, we may allow, without any risk, 

 cotton to lie for 12 or 24 hours at a temperature of 65°f to 

 86°, in a mixture of 100 lbs. water, and 1 to 2 lbs. sul- 

 phuric acid, as is done in clearing the cotton for printing ; 

 when it is well washed with pure water. 



To acidify mordants, sulphuric acid is employed. It is in 

 these cases, however, rendered less deteriorating by mix- 

 ture, but can still be rendered injurious by exposure to a 

 stronger drying temperature. Hence, it is obvious, that such 

 cotton cannot be exposed to strong heat. If sulphuric 

 acid be added to a thick and hot paste of starch, the latter 

 becomes fluid like water ; but . if the paste is previously 

 allowed to cool, and then dilute sulphuric acid is added, no 

 such effect takes place. Mordants which are thickened 

 with starch should therefore be allowed to cool, lest they 

 should be injured by sulphuric acid. By a contrary process 

 the same will be destroyed. Sulphuric acid deprives cotton 

 of the mordant partly by itself, partly in combination with 

 tartar. It may thus, therefore, be employed to renovate 

 injured pieces. It further destroys a quantity of coloured 

 compounds, which is likewise necessary in order to re-dye 

 pieces which are injured in dyeing. 



Both will be farther noticed in the chapter on the renova- 

 tion of injured goods. 



Muriatic acid. — This acid which is employed in chemical 

 manufactures has commonly a yellow colour and a penetrat- 

 ing odour. A colourless is to be preferred to a coloured 





