MERCURY PERCHLORATES. 83 



it) the vacuum-desiccator, w;is that of fine needles, as described by 

 Serullas, and as got by Roscoe presumably, for he makes no mention 

 at all of the form of his crystals. By somewhat slower evaporation 

 in the desiccator, much larger crystals were obtained, and found 

 preferable for analysis, as being more easily freed from mother-liquor. 

 But I took care to use the fine needles in my analyses, as well as the 

 plates. One of the three samples analysed, marked above, II, III, IA r , 

 I cannot say now which, was of fine needles that had formed the first 

 crop, while the other two were of larger crystals that had been the 

 second crop from the same preparation. Sample I was of another 

 preparation. If Koscoe's preparation was a higher hydrate than that 

 I have obtained, it should not have shown itself able, even for a short 

 time, to bear the heat of 100° or the dry air of a desiccator without 

 loss, as he found it to do. 



Beliaviovr of mercurous Perchlorate when heated. — Mercurous Per- 

 chlorate, unlike the mercuric salt, has no melting point. Quickly 

 raised to about 11)0°, the salt becomes partly liquid for a short time, 

 but only from the presence of un volatilised acid along with basic salt. 

 When gradually heated, the salt does not show even this false fusion. 

 At 100°, the crystals of the salt decrepitate. At this temperature, it 

 loses acid only very slowly, so as to be still all soluble in a little w 7 ater 

 after two or three hours heating in an open tube. At about 150°, its 

 crystals slowly intumesce and become opaque. Not only basic salt is 

 then formed, but also a little mercuric salt and a trace of chloride. At 

 170°, for some hours its decomposition goes farther; more mercuric 

 salt is formed and a good quantity of chloride, as well as some chlorate 

 (detected by decomposing with zinc and sulphuric acid). At 200°, 

 white fumes escape, containing mercuric chloride. The more the salt is 

 heated, the more basic it becomes, the redder and the larger is the 

 residue left by water, and the less mercurous nitrate this residue yields 



