pounds, including ones that had not
actually been synthesized. In 1925
The US Patent OfÜce ruled that such
patents were valid. Markush struc-
tures can be described for com-
pounds with substituents at several
positions, and often many thousands
of possible compounds are deÜned in
this way. An important part of chem-
ical database searching is the ability
toÜnd possible Markush structures
to rule out priority in the patent ap-
plication. Chemical drawing pro-
grams can represent such structures.
For example, a bond to the centre of
a ring indicates substitution at any
position on the ring.
Marquis test A widely used pre-
sumptive test that gives a variety of
colour changes with a range of com-
pounds. It is particularly useful for
detecting opiate alkaloids and for
amphetamines and methampheta-
mine. Marquis reagent is a mixture
of methanal (formaldehyde) solution
in water with sulphuric acid. Mesca-
line gives an orange colouration.
With morphine, a violet colour is
produced. Amphetamines give an or-
ange-red colour and methampheta-
mine gives an orange colour. The two
can be distinguished by the Simon
test. The mechanism involves attack
of the aldehyde an a substituted aro-
matic ring to form a carbocation. Fur-
ther reaction forms a coloured dimer
of the original molecule.
marsh gasMethane formed by rot-
ting vegetation in marshes.
Marsh’s test A chemical test for ar-
senic in which hydrochloric acid and
zinc are added to the sample, arsine
being produced by the nascent hy-
drogen generated. Gas from the sam-
ple is led through a heated glass tube
and, if arsine is present, it decom-
poses to give a brown deposit of
arsenic metal. The arsenic is distin-
guished from antimony (which gives
a similar result) by the fact that an-
timony does not dissolve in sodium
chlorate(I) (hypochlorite). The test
was devised in 1836 by the British
chemist James Marsh (1789–1846).martensiteA solid solution of car-
bon in alpha-iron (see iron) formed
when *steel is cooled too rapidly for
pearlite to form from austenite. It is
responsible for the hardness of
quenched steel.mascagniteA mineral form of
*ammonium sulphate, (NH 4 ) 2 SO 4.maser(microwave ampliÜcation by
stimulated emission of radiation) A
device for amplifying or generating
microwaves by means of stimulated
emission (see laser).
massA measure of a body’s inertia,
i.e. its resistance to acceleration. Ac-
cording to Newton’s laws of motion,
if two unequal masses, m 1 and m 2 ,
are allowed to collide, in the absence
of any other forces both will experi-
ence the same force of collision. If
the two bodies acquire accelerations
a 1 and a 2 as a result of the collision,
then m 1 a 1 = m 2 a 2. This equation en-
ables two masses to be compared.
If one of the masses is regarded
as a standard of mass, the mass
of all other masses can be meas-
ured in terms of this standard.
The body used for this purpose is a
1-kg cylinder of platinum–iridium
alloy, called the international stan-
dard of mass.mass actionThe law of mass ac-
tion states that the rate at which a
chemical reaction takes place at a
given temperature is proportional to
the product of the active masses of
the reactants. The active mass of a re-
actant is taken to be its molar con-
centration. For example, for a
reaction
xA + yB →products343 mass action
m