PHYSICS, CHEMISTRY AND ENGINEERING 155 



with the alloy rolled into sheets of from 0.015 to 0.025 inches 

 in thickness is as yet doubtful. We are at present investi- 

 gating this phase of the problem. 



The mechanical properties of the silicon series offers points 

 of particular interest. Here it is seen that the strength 

 increases as the silicon content increases, until the maximum 

 strength is reached with about 4.5 per cent silicon. From 

 this point on, the elastic limit coincides with the ultimate 

 strength and both decrease very rapidly. The curves for re- 

 duction of area and elongation show that the alloys below 2.5 

 per cent are unusually tough, much more so than correspond- 

 ing alloys made by the ordinary methods. 



Of great interest is the critical point that occurs with about 

 2.6 per cent silicon. This point was first observed by the 

 tact that two ingots, containing 2.55 and 2.57 per cent sili- 

 con respectively, were not forgeable but fell into a mass of 

 crystals that apparently had no adhesive strength. As crit- 

 ical points are usually associated with the formation of defi- 

 nite compounds, it is of interest to note that a compound of 

 the formula Fe 19 Si, if it exists, would contain 2.56 per cent 

 silicon, and similarly that a compound of the formula Fe 19 Si 2 

 would contain 4.99 per cent. It was stated above that a crit- 

 ical point in the present case occurs with a silicon content of 

 2.55 to 2.57 per cent. 



Furthermore, it is seen that there is another sudden 

 change at about 5 per cent silicon. Whether this agree- 

 ment is a mere coincidence, or whether these compounds 

 or others, actually exist, has not been definitely de- 

 termined, as cooling curves for these particular alloys are not 

 available. 



In conclusion it should be said that, while it has been pos- 

 sible by the vacuum method to produce iron of unheard of 

 magnetic quality this iron is not yet ready to be put into 

 practical use. It is even doubtful whether it ever will be 

 possible to realize these properties in commercial apparatus. 

 However, this investigation has given a new indication of the 

 possibilities obtainable in the realm of magnetism, and who 

 dare say that this is the end? If it is possible to increase the 

 maximum permeability in one step from 10000 to 50000, we 

 might look forward to permeabilities of 100000 or even 

 more. 



