Aug. 15, 1921 
Sandy Crystals in Ice Cream 
793 
IDENTIFICATION OF THE CRYSTALS AS LACTOSE HYDRATE 
MICROSCOPICAL EXAMINATION 
The ease with which milk sugar usually crystallizes and the very 
characteristic form of its crystals suggest the use of the microscope as 
the most accurate means of identifying it. As mentioned in the earlier 
part of the text it is possible to detect and follow microscopically the 
growth of the crystals in the ice cream. 
For the purpose of identification of the sandy crystals it was necessary 
to have at hand pure specimens of lactose and sucrose crystals. Rather 
than accept the market lactose as standard for recrystallization a quantity 
of pure lactose was obtained by evaporating some milk whey from cheese¬ 
making in a vacuum pan to a concentration of 8 parts by weight of whey 
to 1 part by weight of product. The resulting lactose was filtered and 
purified according to the customary methods. 
The crystalline lactose thus obtained was the a form, or commonly 
recognized lactose hydrate (C 12 H 22 0 n .H 2 0 ). According to Groth (j, 
p. 450) its crystallographic features are— 
Monoclinic-sphenoidal. Cleavage in three directions nearfy at right 
angles. Refractive indices, a = 1.517; /?= 1.542; 7 = 1.550 ±0.005 Bx^c 
= io°, A a== 99 °* 2F = 33-i/ 2°. Sign-, sp. gr. 1.525-1.534. 
Some of these crystals were placed upon a microscopic slide, and a 
photomicrograph was obtained with polarized light. The photograph 
exhibits the characteristic tomahawk-shaped crystals which are always 
presented by a-lactose when the crystals are allowed to develop spon¬ 
taneously below 93 0 C. (j). When they crystallize at 93 °, or a little 
above, lenticular needles appear (7 or anhydride form) (2), which are 
markedly different to the eye. These gradually transform into the 
tomahawk type as the temperature drops below 93 °. The photomicro¬ 
graph of these lactose-hydrate crystals is shown in Plate 138, B. 
The comparison of these pure lactose crystals with those within the 
ice cream in Plate 137, as well as with that of the sandy crystals separated 
in a pure condition from the same ice cream, shown in Plate 138, A, 
shows the sandy crystals to be identical in form with those of pure lactose. 
It is but natural that we should realize the effects shown in Plates 137 and 
138, A, of substances tending to hinder perfect growth of the crystals. 
Also the solvent action of water is evident in the partially dissolved 
facets and less sharp outlines. Otherwise there is no difference in the 
appearance between the crystals in Plate 138, B, and those in the first 
three figures. 
A fully developed crystal of sucrose is shown in Plate 138, C. The 
sucrose crystals were grown within a pectin gel from a supersaturated 
sucrose solution (500 per cent solution) at ordinary temperature. There 
is not the least resemblance between this crystal and those isolated from 
ice cream. 
