1815.] On Todine. 185 
It may be stated, in the first place, against the existence of 
hydro-chlorates, that we must admit tHat on evaporating the water 
in which they are dissolved, they are changed into chlorurets, and 
that by redissolving these we reproduce the hydro-chlorates. » 
It is very true that crystallization is sufficient to change the 
hydro-chlorates of potash, soda, and barytes, into the state of chlo- 
rurets. But this does not happen with the hydro-chlorates of lime 
and magnesia. A high temperature is necessary to deprive the first 
of the whole of its water. And how can we affirm that a part of 
that water is not the result of the oxygen and hydrogen which con- 
stituted the hydro-chlorate ? That of magnesia requires likewise a 
high temperature to be decomposed, and the chlorine finds still 
sufficient hydrogen to be changed into hydro-chlorie acid. 
Here then is a decided case in which hydro-chloric acid, and we 
may add hydriodic acid, are not able to reduce magnesia, though in 
circumstances most favourable to their action. But if we cannot 
deny the existence of hydro-chlorate and hydriodate of magnesia, 
by what certain character can we know that those of lime cannot 
exist at the ordinary temperature of the atmosphere ? 
When a solution of chloruret of calcium is mixed with subcar- 
bonate of ammonia, the chlorine must pass to the state of hydro- 
chloric acid in order to combine with the ammonia. And if we 
ean admit that water is decomposed at the moment of precipitation 
in order to furnish hydrogen to the chlorine, and oxygen to the 
calcium, nothing in that case prevents us from admitting that the 
act of crystallizing is sufficient to convert an hydro-chlorate into a 
chloruret, and that the solution of a chloruret in water converts it 
into a hydro-chlorate ; for it-is the difference of solubility of subcar- 
bonate of lime and hydro-chlorate of ammonia which occasions the 
double exchange of the bases and acids ; and consequently it is on 
account of that difference of solubility that the water is decomposed. 
lf we mix together chalk and muriate of ammonia, we reproduce 
by heat subcarbonate of ammonia and chloruret of calcium. Thus, 
though we refuse to admit that the chloruret of calcium is changed 
into hydro-chlorate by solution in water, we must still allow that 
the elements of water may be separated or united by a trifling 
change of temperature. What I have just said of the hydro-chlo- 
rate of lime applies to most of the other hydro-chlorates and 
hydriodates ; and I might mention other analogous facts. But I ask 
this only to be granted me, that water in certain circumstances may 
be formed or decomposed by the same forces which produce the 
double decomposition of salts. These forces being in general very 
weak, since a slight change in temperature is sufficient to vary the 
nature of double decompositions, it will be obvious that solution in 
water and crystallization may determine the decomposition and 
formation of this liquid. But in that case the reason which I 
assigned in favour of the existence of chlorurets and iodurets dis- 
solved in water, does not appear to me to have the same force. 
It may be alleged, on the other hand, in favour of the existence 
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