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became dark on drying, and yielded a dark coloured liquor in the citric 

 acid factory, a liquor which filtered with difficulty. All these features 

 were very objectionable to the citric acid maker, and led him to prefer 

 concentrated juice to citrate of lime as his raw material. Heating?, by 

 rendering the citrate crystalline, permits of its purification, many of the 

 impurities are removed with the water and can be easily washed away. 

 It seems very important that heat should be used at this stage; it 

 is probablv due to its omission that the earlier experimenters with 

 citrate of lime encountered so many difficulties. 



As soon as the citrate is seen to become crystalline and subside rapidly 

 the heating is stopped, the citrate quickly settles leaving a clear yellow 

 liquid above, this liquid is poured off or syphoned off, as much wa^er 

 being removed as possible. Washing the citrate a few times with hot 

 water is advantageous, this removes the gummy matters which cause 

 the citrate to cake into lumps in drying and which may give rise to 

 darkening in colour and the subsequent production of dark and trou- 

 blesome citric liquors in the manufacture of acid. The earlier samples 

 of citrate contained so much impurity and were so difficult to manipu- 

 late that they found little favour with manufacturers. 



The method of dealing with the citrate at the next stage of the pro- 

 cess will depend entirely upon the scale upon which the manufacture is 

 conducted ; when the operation is conducted on a small experimental 

 scale, the citrate may be thrown upon a stout cloth supported on a sieve 

 or strainer, as soon as the water has drained away the residue is tied or 

 folded securely in the cloth and submitted to pressure, to remove as 

 much water as can be thus got rid of. 



When a large quantity of citrate is made, a filter such as is used in 

 citric acid works, may be employed, this consists of a deal floor with 

 boards round the edge; the floor has one inch splines nailed on it one 

 inch apart, and canvas (36 in. " forfar") is stretched on the splines : a 

 convenient size is 16 ft. x 12 ft. by 1 ft. deep. It should be slightly- 

 tilted and exit holes provided." (Grosjean) The citrate is allowed to 

 drain upon the filter; when draining ceases the substance is put into 

 canvas bags and submitted to pressure. 



On a large scale it will be found more convenient to use filter 

 presses ; by their use the combined operations of filtering and pressing 

 can be expeditiously performed, a great saving of time and labour can 

 be thus effected, while the factory can be rendered much more com- 

 pact owing to the small area occupied by the filter presses as 

 compared with the space requiried for filters and the presses for the 

 bags. 



After as much water as possible has been pressed from the citrate 

 by whatever process is adopted, it has to be dried. This part of the 

 process demands great care, and is attended by considerable risk of 

 loss ; there is great tendency on the part of the citrate, when in a 

 damp state, to ferment ; as a result of this fermentation, the citric 

 acid is destroyed and carbonate of lime, the original chalk from which 

 the manufacture started, is left ; there is little to indicate to the eye 

 that this fermentive change is taking place, so that an unskilled or 

 careless operator may find his finished product to contain no citrate 



