642 ' AGRICULTURAL ANALYSIS 



the caustic soda or potash should be used, it is necessary to know 

 the carbonate and hydroxid content. 



Following are the methods usually employed in examining this 

 class of goods: 



Carbonate and Hydroxid. Method 7. 19 Solutions Required. 

 A half -normal solution of hydrochloric acid; methyl orange and 

 phenolphthalein indicators. 



Determination. Weigh a large quantity of the sample from a 

 weighing bottle, dissolve in carbon dioxid-free water, and make 

 up to a definite volume. Analyze aliquots of this solution. Ti- 

 trate one portion with half-normal acid, using methyl orange as 

 indicator, and note the total alkalinity thus found. Transfer 

 another aliquot of the same size to a measuring flask and add 

 enough barium chlorid to precipitate all carbonate, avoiding any 

 unnecessary excess. Make the volume up to the mark with car- 

 bon dioxid-free water, stopper, shake, and set aside to allow the 

 precipitate to settle. When the liquid becomes clear, draw off 

 one-half by means of a pipette and titrate with half-normal hy- 

 drochloric acid, using phenolphthalein as indicator. This num- 

 ber of cubic centimeters of half-normal acid multiplied by two 

 gives the number of cubic centimeters of half-normal acid cor- 

 responding to the original amount taken. The last figure ob- 

 tained represents sodium or potassium hydroxid and the differ- 

 ence between the first and last figures represents the sodium or 

 potassium carbonate. 



Carbonate and Hydroxid. Method //. 20 Solutions Required. 

 A fifth-normal solution of potassium acid sulfate; methyl 

 orange and phenolphthalein indicators. 



Determination. Dilute with carbon dioxid-free water an ali- 

 quot of the solution as prepared in Method I and add a few drops 

 of phenolphthalein. Add a fifth-normal solution of potassium 

 acid sulfate at the rate of about one drop per second, with con- 

 stant stirring, until the pink color fades out and the solution be- 

 comes colorless. The reading thus obtained (n) represents the 

 sodium or potassium hydroxid and one-half of the sodium or po- 

 tassium carbonate present, since the sodium or potassium car- 



19 Bureau of Chemistry, Bulletin 107, 1907 -.31. 

 10 Bureau of Chemistry, Bulletin 107, 1907 : 32. 



