A FEW OBSERVATIONS 361 



at which time the mill was closed because of the owner giving up 

 the business. This can mean but one thing, namely, that the 

 flour moth in that mill, in every stage of its life, including that of 

 the eggs, was killed by the process. 



A miller must not expect, however, that one treatment will 

 necessarily eradicate all and every pest in the mill. There is the 

 chance that the figuring of the amount required may not have been 

 accurate, or that the mill may not have been properly cleaned 

 beforehand; or that it may become reinfested from some source. 



Effect on Other Insects. A few of our mill pests do not yield 

 readily to this treatment, which is so efficacious against the flour 

 moth. Fortunately they are not insects which are particularly 

 troublesome. We frequently find some of the little red beetles, 

 flour beetles, sometimes erroneously called " weevils," alive in a 

 mill after fumigation. The same is true of the flattish, yellowish- 

 brown " worms" (meal worms) which later turn into black beetles. 

 These two pests are apt to bury themselves in inaccessible places, 

 and in the midst of fine stuff, thereby precluding the possibility 

 of the gas reaching them. However, these insects are of small 

 importance compared with the flour moth, against which this 

 process is especially directed. 



A few observations made in the course of the work may well 

 be given here for the information of millers. 



1. The size of lumps of cyanide makes but little difference, 

 except that the pieces, as shown in the illustration (Fig. 364), 

 should be of convenient size for doing up in bags. The corners of 

 small pieces do not push through the paper as readily as do the 

 corners of large pieces. 



2. Hot and cool acid appear to act with equal rapidity upon 

 the uncovered cyanide, but the temperature of the liquid makes 

 a great difference in the matter of penetrating a double paper 

 sack the cooler liquid penetrating the paper much more slowly. 



3. The make of sacks appears to cause no difference in the 

 time required for the acid to penetrate to the cyanide, so long as 

 the sacks are of manila, and are not of heavy material, such as is 

 used for sugar sacks. The latter should be avoided. Cloth sacks 

 should never be used. 



4. Mills should never be fumigated for less time than one night. 



5. Twenty-five seconds elapsing between the dropping of 

 cyanide and the first giving off of gas in a fatal amount is a con- 

 servative time estimate, resulting from practical tests with the 



