The effectiveness and the advantages and disadvantages of various substances and
compounds that are used or offered in the market for use in the radiators of
automotive vehicles as anti-freeze materials are discussed. These include
alcohols, glycerine, salts, oils, sugars, and glycols.
Properties affecting the suitability of a material or compound, or solutions of
them with water to afford protection against freezing at atmospheric
temperatures that are likely to be encountered are their heat capacity,
freezing-point, boiling-point, specific gravity, viscosity, volatility,
solubility, tendency to decompose at the boiling-point, inflammability,
corrosive action upon metals, tendency to attack rubber, general availability,
and price.
The freezing-points of solutions of different materials vary widely at the same
concentrations, or proportions to water, and also with variation of their
concentration. Determinations of the freezing-points as made at the Bureau of
Standards are given in charts. The freezing-points also vary with the specific
gravity, and determinations of these points are given. Large differences exist
in the initial viscosity of water, oils and aqueous solutions of glycerine,
glycol and honey, and in the rate of increase of viscosity with decrease in
temperature. Curves based on viscosity determinations for such liquids over a
wide temperature range are shown.
Solutions of the salts of sodium, calcium and magnesium have much lower
freezing-points than the sugar solutions and at much lower concentrations and
afford protection at considerably lower minimum temperatures. Glycerine and
ethylene glycol give protection at almost as low minimum temperature as calcium
chloride, which is the most efficient of the salts, but only at about double the
concentration. Wood alcohol and denatured alcohol rank next in effectiveness, at
concentrations of 50 and 70 per cent by volume, and resist freezing at a
temperature of -40 deg. fahr.
Alcohol has several virtues as an anti-freeze material but boils at 172.4 deg.
fahr., which results in its rapid loss by evaporation and limits the use of
devices for maintaining high engine-temperature. Kerosene, on the contrary, has
a high boiling-point that may result in serious overheating of the engine in
mild weather. Other objections to its use are its odor and inflammability and
its action upon rubber. Lubricating-oil and the solutions of sugar have high
viscosity at low temperatures, which causes slow circulation of the cooling
medium unless the passages in the cooling-system are ample.
Commercial distilled glycerine that is free from electrolytes and is practically
neutral has no corrosive effect on metals and does not injure rubber; its
evaporation is negligible and it can be recovered at the end of the cold season
and used again. If alcohol that is lost by evaporation must be replaced four or
five times in a season, glycerine at four times the price is less expensive even
for one season. Glycerine solutions of higher specific gravity than 1.144 are
not recommended for use in cars having thermosiphon circulation, because of
their high viscosity at low temperatures.
Ethylene glycol is made indirectly from petroleum or ethyl alcohol and sold in
the winter of 1925 and 1926 at about the same price as glycerine. It gives more
protection against freezing than either glycerine or denatured alcohol solutions
of the same volume-per cent, is practically non-volatile, is no more corrosive
than water, and is only slightly more viscous at low temperatures than
denatured-alcohol solutions of equal concentrations.
In testing solutions for determination of their freezing-points, care must be
taken to avoid the phenomenon of undercooling, that is, the tendency to resist
freezing under some conditions at temperatures considerably below the maximum
temperature at which crystals can begin to form. Apparatus used at the Bureau of
Standards for making such determinations is illustrated and described. The
present procedure and a proposed new method for testing the corrosive action of
anti-freeze liquids are also described.
