164 CHYMISTRY APPLIED TO AGRICULTURE. 



When nothing niore than the extraction of the citric 

 acid is required, the process is conducted in the following 

 manner. Sulphuric acid diluted with six or seven times 

 its weight of water is thrown upon the citrate, the mixture 

 being stirred as the citrate is turned in ; when decomposi* 

 tion has fully taken place, the citric acid swims above the 

 insoluble sulphate of lime which has been formed; the 

 whole is filtrated and the deposit washed ; the water of the 

 washing is added to the acid, and evaporation is carried 

 on in pewter vessels : this operation may be commenced 

 by boiling the liquor rapidly, but in proportion as this 

 becomes thickened the action must be diminished ; when 

 the acid has acquired the consistency of a sirup it is re- 

 moved from the fire and left to crystallize. After the 

 crystals have been removed from the mother water, ten or 

 twelve times its own weight of water is added to it, and it is 

 then treated in the same manner as the lemon juice. 



In order to obtain the crystals of citric acid perfectly 

 pure, it is necessary to repeat the processes of solution, 

 filtration, and evaporation, several times. When these 

 operations are skilfully performed, the juice of the lemon 

 yields about \ of its weight in citrate of lime, and -j\j of 

 citric acid in crystals. 



Citric acid is very soluble in water, and advantageously 

 supplies the place of lemon juice for domestic purposes, 

 and in the arts, both by its being freed from mucilage, 

 which renders the juice liable to undergo speedy changes, 

 and from the diminution of its bulk by concentration. 



To give a flavor to food, citric acid is much more agreea- 

 ble than vinegar, on account of the aromatic particles it 

 contains ; dissolved in water it forms a very wholesome 

 drink : about 30 grains of this acid dissolved in a pint of 

 water and sweetened with sugar, composes an excellent 

 lemonade. From its refreshing and antiputrescent proper- 

 ties, it is invaluable during the hot months, and especially as 

 an article for sea stores of vessels in warm latitudes. 



Citric acid has also its peculiar uses in the arts; like the 

 oxalic acid, it is employed in forming reserves in printed 

 goods, and in removing spots of ink or rust. 



When the coloring principle of the saffron {carthamus 

 tinctorius) is dissolved by an alkali and precipitated by 

 citric acid, it produces, upon silk, an orange, scarlet, or 

 light-red color ; when thrown down in the same manner 

 upon a white, oily surface, it constitutes the vegetable red 

 or rouge. 



