CHA 
amphibious and land animals, as the heads, 
and vertebra?, of crocodiles, and teeth of 
elephants. Chalk hills never rise to a higher 
elevation than three or four hundred feet, 
and are at once distinguishable by the 
smooth regularity of their outline, and their 
remarkable tendency to form cup-shaped 
concavities. Ridges of chalk, in England 
at least, are always bordered by parallel 
ranges of sand or sandstone, beneath and 
alternating with rvhich are situated the beds 
of fullers-earth. Chalk hills are also singu- 
larly characterized by their dryness and 
their verdure : the most porous sandstone 
is scarcely so deficient in springs of water, 
and yet except upon almost perpendicular 
descents, the white surface of the chalk is 
uniformly covered with fine turf or wood. 
The chalk hills in England occupy a 
greater extent than in any other country, 
they run in a direction nearly from east to 
west parallel to each other, and separated 
by ranges of sand-stone, and low tracts of 
gravel and clay. The most northern and 
loftiest range of chalk commences at the 
promontory of Plamborough-head, in York- 
shire, and proceeds westward for nearly 20 
miles. In the county of Lincoln are some 
fragments of a ridge near Clrantham. Two 
ridges traverse the midland counties, and 
reach as far west as the borders of Oxford- 
shire ; these ridges are no where so conspi- 
cuous as in the county of Bedford, where 
they approach near to each other, being 
only separated by the Woburn and Ampt- 
hill range of sand stone. The country 
lonth of the Thames also contains two 
ridges, tiie one commencing at the North 
and South Foreland, passing through the 
nortli of .Kent, the middle of Surry, and 
the north of Hampshire, and including the 
North Downs of Banstead, Epsom, &c. : 
the other, commencing near Hastings and 
at tlie lofty promontory of Beachy-head, 
passes through Sussex and the south of 
Hampshire, uito Dorsetshire, including the 
South Downs. The north part of France 
also abounds in chalk: it is besides met 
with in some of the Danish islands in the 
Baltic, and in Poland. 
The uses of chalk are very extensive: 
the more compact kinds are used as build- 
ing stone, and aie burnt to lime (nearly all 
the buildings in London being cemented 
with chalk-mortar) ; it is also largely em- 
ployed in the polishing of metals and glass, 
in constructing moulds to cast metal in, by 
carpenters and others as a material to mark 
with, and by starch-makers and chemists 
CHA 
to dry precipitates on, for which it is pern 
liarly qualified on account of the remark- 
able facility with which it absorbs water. 
Chalk stones. It is well known that 
concretions occasionally make their appear- 
ance in joints long subject to gout. These 
concretions, from their colour and softness, 
have received the name of chalk-stones. 
They are usually small, though they have 
been observed of the size of an egg. It had 
long been the opinion of physicians that 
these concretions were similar to the urinary 
calculi. See Calculi. 
Of course, after the discovery of uric 
acid by Scheele, it was usual to consider 
the gouty chalk-stones as collections of that 
acid. They were subjected to a chemical 
analysis by Dr. Wollaston in 1797, who 
found them compo ed of uric acid and 
soda. Gouty concretions are soft and fri- 
able. Cold water has little effect upon 
them; but boiling water dissolves a small 
portion. If an acid be added to this solu- 
tion, small crystals of uric acid are depo- 
sited on the sides of the vessel. These 
concretions are completely soluble in pot- 
ash when the action of the alkaline solu- 
tion is assisted by heat. When treated 
with diluted sulphuric or with muriatic 
acid, the soda is separated; but the uric- 
acid remains, and may be separated by fil- 
tration. The liquid, when evaporated, 
yields crystals of sulphate or muriate of 
soda, according to the acid employed. 
The residuum possesses all the characters of 
uric acid. 
When uric acid, soda, and a little warm 
water, are triturated together, a mass Is 
formed, which, after the surplus of soda is 
washed off, possesses the chemical proper- 
ties of gouty concretions. 
CHALLENGE, in law, is an exception 
made to jurors, who are returned to a per- 
son on a trial. 
This challenge is made either to the 
array, or to the polls .- to the array, when 
exception is taken to the whole number of 
jurors impannelled ; and to the polls, when 
an exception is made to one or more of the 
jury as not indifferent. 
. Challenge to the jurors is likewise divided 
into challenge principal or peremptory, and 
challenge for cause ; that is, upon cause or 
reason alleged. Challenge principal, is 
what the la\v allows without any cause al- 
leged, or further examination : as a pri- 
soner arraigned at tire bar for felony may 
challenge peremptorily the number allowed 
him by law, being twenty, one after an 
