Mat 2, 1912. 



The Weekly Florists' Review. 



21 



^ith the hydrocyanic acid gas as fast 

 ^B it formed, there might be little or 

 none of the gas left to do its work. 

 Therefore, use a practically pure potas- 

 sium cyanide. 



The Sulphuric Acid. 



Perhaps the sulphuTic acid is the 

 most variable of the three factors used 

 in fumigation. At least, it is exceed- 

 ingly important that it should meet 

 certain requirements if the treatment 

 is to be satisfactory, as the use of a 

 wrong grade of acid is liable to cause 

 injury to foliage. Commercial sulphuric 

 acid is satisfactory, provided it con- 

 tains no nitric acid and is of the 

 strength known as 66 degrees Baum6. 

 Such an acid should average ninety- 

 three to ninety-four per cent of actual 

 sulphuric acid, the other six or seven 

 per cent consisting of impurities of 

 various kinds. Sulphuric acid is made 

 either from free sulphur or from sul- 

 phur combined with iron or copper and 

 known as pyrites. Ordinarily the py- 

 rites used contains arsenic, etc., to 

 some extent. In the manufacture it be- 

 comes mixed with fumes of nitric acid 

 and, when pyrites is used rather than 

 sulphur, much more nitric acid becomes 

 mixed with the sulphuric acid produced 

 than in the case where sulphur is 

 taken. The nitric acid can be removed 

 by refining, of course, but this in- 

 creases the cost. 



The danger in having nitric acid 

 present is that it is energetic in its 

 action and also volatilizes readily. Ac- 

 cordingly, when sulphuric acid contain- 

 ing it is added to water, the heat pro- 

 duced begins to volatilize the nitric 

 acid, and when the cyanide is added it 

 increases the heat, and the passing off 

 into air of the hydrocyanic acid gas 

 'Causes the nitric acid also to pass into 

 the air. When this condenses again on 

 the leaves its action is vigorous and 

 also extremely injurious, causing burn- 

 ing wherever it touches. 



For the greatest economy of gas pro- 

 duction, then, the acid should be of the 

 grade known as 66 degrees Baum6, and 

 in addition it should be entirely free 

 from nitric acid. 



Proportions of the Ingredients. 



Of the water little need be said. It 

 is, of course, possible that waters con- 

 taining impurities might include some- 

 thing which could modify the chemical 

 process to some extent, but this, at 

 least in New England, would in all 

 probability never be the case. 



The proportions to use of these dif- 

 ferent materials have been variously 

 given at different times. One writer, 

 who has been widely followed, says: 

 "A half more acid, liquid measure- 

 ment, than cyanide, and a half more 

 water than acid are used." Another 

 suggests a 1-2-3 ' formula. Eecent 

 studies on this point have been based 

 on the principle that when one chemi- 

 cal acts upon another to produce a 

 third, the amount actually used is al- 

 ways the same, and the presence of 

 more than enough of either simply 

 means a surplus of it left unchanged 

 at the completion of the combination. 



The actual process of combination of 

 the chemicals is expressed as follows: 



2KCN + HjSOi = K,S04 4- 2HCN. 

 Potasslnm cyanide 4- hydrogen sulphate = po- 

 tassium sulphate + hydrocyanic acid. 



An Excees of Acid. 



If we take an ounce by weight of 

 the potassium cyanide, we find that 



Prof. Henry T. Feniald. 



three-quarters of a fluid ounce of sul- 

 phuric acid is sufficient to give hydro- 

 gen enough to combine with all the 

 cyanogen there is in the potassium cy- 

 anide. On the other hand, a little of 

 the hydrocyanic acid may dissolve in 

 the water present instead of passing 

 off into the air as a gas, and would 

 thus be lost, so far as use goes. The 

 addition of another quarter of an 

 ounce of acid will heat the water more, 

 and tend to drive the gas out, so that 

 for this reason it seems to pay to use 

 a little excess of acid over what is 

 needed for the chemical process, to get 

 more of the gas. 



Too much excess of acid, however, 

 produces trouble in a different way. 

 The formula given shows that potas- 

 sium sulphate is formed in addition to 

 the hydrocyanic acid gas. Now, potas- 

 sium sulphate, though a solid, dissolves 

 in the water present, but if there is 

 much spare sulphuric acid also present, 

 less of the potassium sulphate dis- 

 solves, and instead it tends to form a 

 crust covering the pieces of potassium 

 cyanide not already acted upon, so 

 that the sulphuric acid cannot reach 

 these pieces to combine with them and 

 produce more gas. For this reason, 

 then, too much acid is as undesirable 

 as too little, and if after a fumigation 

 has been completed there is a solid or 

 a slushy substance left in the dish, this 

 indicates that either too little water or 

 too much acid was used. 



The Action of the Water. 



At present, then, the proper amounts 

 to use seem to be: One part by weight 

 of cyanide, and one part by measure of 

 acid. 



Water is not absolutely essential to 



the production of hydrocyanic acid gaa 

 by the action of sulphuric acid on po- 

 tassium cyanide, as the acid could be 

 poured directly upon the cyanide, and 

 some gas be given off. The process 

 would quickly come to an end, how- 

 ever, in this case, as the potassium sul- 

 phate formed would so coat over the 

 cyanide that the acid would either fail 

 to reach it or would do its work too 

 slowly. Water is useful in dissolving 

 both the cyanide and the potassium 

 sulphate produced, and in hastening 

 the chemical reaction, which is of im- 

 portance, as the maximum amount of 

 gas is needed as quickly as possible for 

 effective results. If too little water ia 

 present the potassium sulphate tending 

 to coat the cyanide is not dissolved, 

 and this delays the process if it does 

 not in part prevent it. Then the heat 

 produced by mixing the acid and the 

 water is a great advantage, as it has- 

 tens the chemical reaction. 



It is evident that too little water 

 will prevent the production of the 

 maximum amount of gas. Experiment 

 shows that too much water acts in the 

 same way, more of the gas entering 

 the water and thu^ reducing the 

 amount in the air. A series of tests 

 using varying amounts of water has 

 shown that for the best results there 

 should be three times as much water as 

 acid, and the best proportions of all 

 three materials to use, therefore, be- 

 come: 



Cyanide, one part by weleht. 

 Acid, one part by measure. 

 Water, three parts by measure. 



The Bight Order in Mixing. 



It is desirable to utilize the heat pro- 

 duced by the addition of the sulphuric 



