398 Foreign and Miscellaneous Intelligence. 



it evolved white vapours in some abundance ; it was then mixed with 

 four or five times its volume of concentrated sulphuric acid, and dis- 

 tilled in a small retort, to which a receiver had been adapted. The 

 mixture became coloured, and when boiling, evolved chlorine and 

 oxygen ; but a small quantity of the perchloric acid escaped decom- 

 position, rose in vapours, and condensed in the receiver, which was 

 purposely cooled. Thus distilled, this acid is solid, it contains no 

 sulphuric acid ; exposed to air, it rapidly attracts water, and at the 

 same time evolves dense white fumes. When melted and poured into 

 water, each drop hisses like hot iron. It melts at 45 C. (113 F.) 

 It appears in two forms, either massive, or in long prisms, appa- 

 rently quadrangular, and terminated by dihedral summits : the latter 

 form is, without doubt, that which contains the minimum of water, 

 and is consequently the most volatile. 



Several precautions are required in procuring with certainty the 

 crystallized acid. The sulphuric and perchloric acid are to be in- 

 troduced successively by a long tube into a small retort not tubu- 

 lated, the neck of which is to be introduced (without a cork) into a 

 bent tube contracted at the extremity. On applying heat, the liquid 

 boils, and is by little fire preserved in that condition ; a portion of the 

 acid soon flows slowly over and solidifies in the tube, which it is 

 sufficient to cool with water. The process must be stopped before 

 the mixture is discoloured, and as soon as a drop of liquid passes 

 over and retains its fluid state, otherwise water will distil and re- 

 dissolve the crystals forming the liquid and non-fuming acid. For 

 the same reason, only small quantities should be operated on at 

 once, not surpassing eight or ten grammes (140 gr.) of perchloric 

 acid. 



Perchloric acid may be concentrated in a retort, by care, almost 

 like sulphuric acid : the first portions are merely water. It has thus 

 been carried to a s. g. of 1.65, and may perhaps be urged further. 

 In this state it evolves some vapour in the air : it boils at 200 C. 

 (392 F.) If, when boiling, dry paper be held in its vapour close 

 to the aperture of the vessel, it inflames vividly. Of this strength 

 ten parts exposed to air attracted 1*8 parts of water in twenty-four 

 hours, and in ten days had attracted 8 parts*. 



5. STRENGTH TEST FOR BLEACHING POWDER. 



The necessity of having a means of ascertaining the chlorine 

 strength of bleaching powder has been felt so strongly, that many 

 persons have turned their attention to the discovery of an unexcep- 

 tionable process for the purpose ; and the use of sulphate of indigo, 

 of salts of manganese, and of the chlorometer apparatus of Gay 

 Lussac, is consequently well known to all who are concerned in the 

 use of that chemical production. M. Marozeau, amongst others, 

 has sought to obviate the objections belonging to all the processes 



* Aim. de China., xlvi. 294. 



