PB0P0B1 ION OF CHEMICALS. 35 
Bolves the potassium sulphate as it Forms and prevents it from coating 
tlit* cyanid not yet in solution. In the presence of an Insufficient 
amount of water, the potassium sulphate is not completely dissolved, 
but forms a coating on the pieces of cyanid, preventing the Bulphuric 
acid from penetrating to it, and thereby retarding, or even in part 
preventing, the reaction. In such cases this undissolved potassium 
sulphate usually congeals, causing the pots to "freeze." The phe- 
nomenon always occurs where the formula is I 1 I, or where the 
Bame amounts of water, acid, and cyanid are used. On agitating 
the congealed residue by stirring, it is almost always possible to find 
small pieces of undissolved cyanid enveloped in a coating of the 
potassium sulphate. Ordinarily, when the residue is stirred the 
particles of cyanid arc 4 removed, to some extent, from this envelope 
of potassium sulphate, allowing some of the unused acid to reach 
them, and thus evolving a small amount of gas without the addition 
of more acid. Under these conditions, however, the reaction is 
never complete, and it is highly desirable therefore to add sufficient 
water at the beginning to dissolve all the potassium sulphate. 
From this last statement, as well as the data presented under the 
heading "The effect of too great an excess of acid" (p. 34), it is seen 
that the concealing or "freezing" of generating jars is due to either 
or both of two conditions: (1) An insufficient amount of water to 
completely dissolve the sulphate of potassium, or (2) a large excess 
of sulphuric acid, whereby the water is rendered less capable of t aking 
into solution the same amount of sulphate as it otherwise would. 
Another very important function of the water in the reaction is 
the heat produced by the union of the sulphuric acid and water. 
Potassium cyanid introduced into this heated mixture gives off hydro- 
cyanic-acid gas much more quickly and thoroughly than at a lower 
temperature, and in field work rapid generation of gas is essential. 
THE EFFECT OF DIFFERENT PROPORTIONS OF WATER ON THE TEMPERATURE OF THE CAS. 
Anyone who has watched the escaping gas and steam from the 
reaction of potassium cyanid and sulphuric acid wherein different 
proportions of water were used could not fail to notice that the 
violence with which the generation starts and the gas is given off is 
apparently greatest with the smaller proportions of water. Fumi- 
gators are aware of this, and commonly increase the proportion of 
water when using large amounts of cyanid. Practice has demon- 
crated that with a greater proportion of water the Injurious effect of 
the resulting gas on the leaves and fruit is materially lessened. The 
lessening of the injury has been attributed to the fact that the escap- 
ing gas was Less heated when large proportions of wafer were used. 
In order to clear up this point an experiment was performed, the 
results of which are given in Table II. 
