320 KANSAS CITY REVIEW OF SCIENCE, 



Says the Boston Journal of Chemistry : " Mr. Poirot, having observed that 

 the immense tracts of worm-wood (sage brush) upon the American plains are 

 free from insects of every description, in experimenting with the plant as a 

 preventive of phylloxera. He finds no difficulty in cultivating the worm-wood, 

 and he proposes to mix the stalks with manure, or simply bury them in the 

 ground in the neighborhood of the vines. His suggestions have been sent to the 

 Phylloxera Committee of the French Academy." 



CORROSION OF IRON UNDER STEAM PRESSURE. 



An occurrence not uncommon in steam engines, is the destruction of the 

 cast-iron directly exposed to the action of the steam, so that it can be readily cut 

 with a knife, like black lead. This destruction is not confined to cast-iron alone, 

 but to wrought-iron also, for many through bolts, such as follower bolts in pistons, 

 are eaten away to such an extent that it seems as though they had been exposed 

 to the action of acids. 



The cause of the troubles noticed, which are not mentioned as any recent 

 discovery, is generally attributed to the lubricating oils, or the tallow used for 

 lubrication. It is asserted that the methods of refining these' leaves a residue of 

 free acid that in time acts as above stated, and the remedies urged are the sub- 

 stitution of pure fat, such as suet in a natural state without having been ren- 

 dered. 



As a matter of fact, all true animal fats — solid fats — contain three acids, 

 margaric, stearic and oleic, and these are active, so far as regards their acid con- 

 stituents at ordinary temperatures. Every engineer is aware that the mere pres- 

 ence of cold tallow, on brass work for instance, turns green, from the deposi- 

 tion of verdigris — which is the "rust of brass " — upon it. This free acid theory 

 is an assumption of our own, for chemists do not recognize the existence of the 

 free acids named, in fats, but assert that they are only liberated in the process of 

 soap-making or saponification of the fats by contact with an alkali. However 

 this may be, it is difficult to account for the destruction of metal surfaces in the 

 manner named, and the prompt action of animal grease upon copper or brass, 

 unless free acid is present, for it presents all the appearance of it. 



It would seem, therefore, that the methods of preparing lubricating com- 

 pounds are not directly at fault, but that under certain conditions, such as heat 

 and moisture, decomposition of the structure may be set up with injurious effect. 

 These conditions are present in the steam engine. At a pressure of seventy-five 

 pounds — not at all uncommon nowadays — the temperature is 308°, which, if not 

 enough to set up destructive distillation completely, may partially effect it or in 

 such degree that the surfaces of iron are attacked. 



It has been found that pure suet unrendered causes as much injury as com- 

 mercially prepared fats, though all irons are not as readily corroded as others ; 

 some escape entirely. 



