584 AGRICULTURAL ANALYSIS 



determinations. Evidently the acid will not be chemically pure, 

 because the sodium chlorid is not absolutely insoluble in hydro- 

 chloric acid; but a portion tested with silver nitrate will prove 

 that the sodium, together with any other bases which may have 

 gone through the filter, has been completely converted into per- 

 chlorate, and unless the original chlorate contained some potas- 

 sium or on evaporation the acid was exposed to the fumes of 

 ammonia, the residue of the evaporation of a portion is easily 

 and completely soluble in 97 per cent, alcohol, and its presence 

 is, therefore, unobjectionable. One cubic centimeter of the acid 

 thus obtained gives on evaporation a residue of only 0.036 gram, 

 which is completely soluble in 97 per cent, alcohol. 



Caspari's acid under similar treatment gave a residue in one 

 case of 0.024 gram and in another 0.047 gram. If, however, a 

 portion of pure acid be required, it may be obtained by distilling 

 this product under diminished pressure, and, as Caspari has 

 shown, without great loss, providing the heat is regulated ac- 

 cording to the fumes in the distilling flask. 



Some modification of the above treatment will be found neces- 

 sary in case the sodium chlorate contains any potassium as an 

 impurity, or if the latter has been introduced from the vessel in 

 which the fusion was made. In these circumstances the hydro- 

 chloric acid would not suffice for the removal of potassium, since 

 a trace might also go over with the sodium, and thus on evap- 

 oration a residue insoluble in 97 per cent, alcohol be obtained. 

 To avoid this difficulty, the mixture of scdium perchlorate and 

 chlorid, after treating with hydrochloric acid for the reduction 

 of the residual chlorate, being reduced to a fine powder, is well 

 digested with 97 per cent, alcohol, which dissolves the sodium 

 perchlorate, but leaves the chlorid, as well as any potassium salt 

 insoluble. By giving the alcohol time to become saturated, which 

 is facilitated by stirring, it is found on filtering and evaporating 

 that an average of about 0.2 of a gram of sodium perchlorate is 

 obtained for every cubic centimeter of alcohol and that the pro- 

 duct thus obtained is comparatively free of chlorids, until the 

 perchlorate is nearly all removed, when more of the chlorid seems 

 to dissolve. This treatment with alcohol is continued until on 



