Kreider — Quantitative Determination of Perchlorates. 287 
Art. XXX.—The Quantitatwe Determination of Per- 
chlorates ; by D. ALBERT KREIDER. 
__ [Contributions from the Kent Chemical Laboratory of Yale College—XLIV.|] 
THE method usually employed for the quantitative determina- 
tion of perchlorates, by igniting to the chloride and weighing 
the halogen as the silver salt, is indirect and subject to error, 
especially as my experience proved, where the free acid is to 
be determined and where, consequently, an alkali which is apt 
to contain chloride is used to form the salt for the ignition. To 
purify the salt for this method only adds to the complication, 
and therefore a more satisfactory process was sought. In a 
recent article* from this laboratory by Professor Gooch and 
myself, a method for the detection of alkaline perchlorates 
associated with chlorides, chlorates and nitrates was detailed, with 
mention of certain efforts towards a quantitative determination. 
As throwing light upon the peculiar properties of perchlorates, 
and as an introduction to the satisfactory method which I have 
finally developed, some of the results of these earlier efforts 
will here be given. 
_ In studying the properties of perchloric acid in the form of 
its potassium salt, we found that when treated with potassium 
iodide in the presence of boiling phosphoric acid, no reduction 
of the perchlorate is effected ; unless indeed, the boiling be 
continued till the temperature rises to 215° to 220° C, where 
the meta-phosphoric acid begins to form. But when the meta- 
phosphoric acid (made by heating the syrupy ortho-acid to 360° 
C) is directly applied in the presence of potassium iodide and 
kept at a temperature of about 200° C, iodine is copiously 
evolved. To test this reaction quantitatively a number of experi- 
ments were made in an apparatus consisting of a retort, into 
the tubulature of which a glass tube was carefully ground and 
prolonged so as to reach to the bottom of the bulb and serve for 
the passage of a current of carbon dioxide, used to expel the 
air and carry the iodine into the receiver. The neck of the 
retort was bent so as to reach to the bottom of an Erlenmeyer 
receiving vessel, containing a solution of potassium iodide, 
which was trapped by a side-necked test tube. After introduc- 
ing the perchlorate with the iodide and meta-phosphoric 
acid, all air was expelled by carbon dioxide and heat applied. 
- The iodine collected in the receiver was titrated with decinormal 
thiosulfate, from which the perchlorate was calculated. 
Table I gives the results of several experiments performed 
in this way, which prove that even with a large excess of potas- 
* This Journal, vol. xlviii, p. 38. 
