Of the iron-carbon alloys of compositions lying to the right of the line UV, we find the case to be different, for each one of them has more than the 1.7% of carbon which is the maximum amount which “gamma” iron can retain. Now the lowest temperature at which any iron-carbon alloy can exist without freezing is slightly above 2066° F., and there is but one composition—95.7% of iron and 4.3% of carbon—which can survive until _this_ low temperature is reached. A content of 4.3% of carbon then, is the greatest and also the least concentration which Nature will allow to remain molten down to this minimum temperature. This 4.3% carbon composition which is the lowest melting, i.e., the easiest melted alloy, is called the “eutectic” alloy from Greek words which mean “well melting.” This eutectic composition may be said to divide or rather subdivide this group of alloys into two groups, those containing between 1.7% and 4.3% of carbon, and those which have 4.3% and over. As stated before, freezing is not an instantaneous but a progressive process. During the freezing period of any of these alloys which have over 1.7% of carbon the _still liquid portion_ which remains after freezing begins to become smaller and smaller in quantity as freezing progresses just as it did in alloys of the “_solid solution_” group. And as Nature allows a concentration of 4.3% of carbon as the highest concentration at the minimum temperature the very last of the remaining liquid of every alloy eventually gets to this eutectic composition just before the alloy freezes. Those to the left of the eutectic or exact 4.3% composition do so by the gradual freezing out of iron containing the maximum or 1.7% of carbon, i.e., iron is taken out faster than carbon, hence there is gradual concentration of carbon in the remaining liquid. This goes on until 4.3% is reached. The compositions to the right of the line WX throw out the chemical compound, Fe_{3}C, which contains 6.6% of carbon, whereby carbon is eliminated faster than iron and the desired 4.3% carbon alloy is arrived at from the other direction. To illustrate, take, say, the composition represented by the vertical line at 3% carbon and 97% iron. As the molten alloy cools it reaches the temperature 2330° F., at which temperature the vertical line representing the 3% carbon composition cuts the line AB. Here the alloy begins to freeze by the separation of small crystals of solidifying iron containing definite amounts of carbon.[11] But as the carbon thus taken along by the freezing crystals of iron is always less than 1.7%, a proportionally greater amount of iron than carbon is removed from the unfrozen part of the alloy and the remaining liquid or unfrozen part, therefore, is left with slightly more than the 3% of carbon with which it started. Footnote 11: