18 
To determine the difference between these, we use the 
polarimeter. Ifa ray of polarized light is passed through 
cane sugar, the plane of polarization turns to the right, 
while with a solution of grape sugar it is the reverse. In 
choosing a sugar, choose one with large crystals, and 
without much granular matter. If sugar contains much 
moisture, it should be rejected. Under the microscope, 
with low power, the crystals of cane sugar are seen to be 
six-sided oblique prisms, while the grape sugar exists in 
acicular tufts. In the latter, too, sugar mites are sometimes 
found ; making the sugar unfit for use. To discover them, 
dissolve a teaspoonful of sugar in a wine glass full of warm 
water, and examine the deposit at the bottom of the tube. 
‘‘Raw’’ sugars are much superior to refiner’s ‘‘ pieces,” as 
the former contain much less grape sugar; though the 
‘« pieces’ may be lighter in colour, they are of less dietetic 
value. Coffee is adulterated with roasted grain, raspings of 
loaves, stale sea biscuits, and the like. Chicory is also 
much used, and is itself adulterated; indeed, ground 
chicory can be bought at a cheaper rate than the dried 
root itself. Good coffee, when ground, if squeezed, should 
not form a cake; and if a spoonful is dropped into 
a tumbler of water, it ought to float on the top; if it sinks, 
it is bad. Many of the adulterations of coffee may be seen 
under the microscope. From the examination of the 
various samples obtained in Croydon, it does not appear 
that adulteration is very extensive. 
Some discussion took place on the question of Mr. 
Kent’s paper, on ‘‘ Pond Infusoria,” read at a previous 
meeting of the Club, in which Dr. Carpenter, Mr. J. 8. 
Jounson, and others took part. ‘ 
The PresipEnt remarked that it was pleasant to see the 
Hon. Sec., Mr. Long, once more at his post, after his 
serious illness. 
The following gentlemen were elected members of the 
Club :—Messrs. C. Penley, Horace W. Petherick, Edward 
Fagg, and Richard J. Dickens. 
March 20th, 1872.—On ‘Tue Poxarization or Lieut,” by Dr. 
Meymort Tipy.—The lecturer described, in rapid summary, 
the various discoveries respecting polarized light, taking as 
his basis the undulatory theory. Referring to the strong 
analogy between light and sound, he stated that there 
appeared to be but one force pervading all nature; but 
this force takes various forms. After describing the con- 
stitution of a ray of light, the lecturer proceeded to deal 
