A. H. Lees 145 



In considering these plotted results it is probable that as soon as 

 the paraffin wetting rises above zero the mixture would have a slight 

 tendency to scorch and a much greater tendency when wetting by 

 paraffin attained a higher value than wetting by water. Considering 

 the results obtained with tap water first it will be noticed that with 

 only I % of soap no wetting by water could be obtained and that with 

 increase of paraffin the wetting by it increased to a maximum. The 

 lower percentages therefore would be unsafe and the higher percentages 

 would certainly produce scorching effects. 



With 1 % soap there would be a slight tendency to burn even with 

 only 1 % of paraffin but in practice, owing to the small quantity of 

 paraffin present, this does not occur. With larger quantities such as 

 5 % and over burning does actually take place. With 1| % of soap 

 the doubtful point is only reached with 10 % of paraffin and there would 

 be no serious danger until 20 and 25 % was reached. For 2 % of 

 soap probably all strengths would be safe, though for tender fohage 

 there might be some small risk above 5 % of paraffin. With distilled 

 water the doubtful points occur at 5 % for | % soap, at 15 % for 1 % 

 soap, at 20 % for 1| % soap and at 25 % for 2 % soap. 



It will be noticed that the h % distilled water results are intermediate 

 between the 1 % and 1|^ % tap water results. This indicates that in 

 water with a hardness of 12° (such as we have in Bristol) about f % 

 soap is used up in precipitating the metalHc salts which cause hardness. 

 That amount of soap is therefore wasted. (This represents about 

 f lb. per 10 gallons and involves a loss of about one penny for that 

 amount of spray fluid.) 



From a practical point of view the following recommendations may 

 be drawn from these results. Using tap water of a hardness of 12° or 

 using soft water the amounts of soap to be used for various percentages 

 of paraffin in order to obtain a safe mixture are shown in the following 

 table : — 



Table II. 



Tap water Soft water 



% paraffin % soap required % paraffin % soap required 



10—25 2 20—25 2 



2—10 li 10—20 1^ 



1 1 5—10 r 



— _ 1_5 ^ 



In cases where the hardness of water is more or less than 12° the 

 greater or less quantity of soap may be approximately calculated by 

 assuming that 12° hardness equals | % soft soap Thus for water of 



