pounds, including ones that had not
actually been synthesized. In 1925
The US Patent OfÜce ruled that such
patents were valid. Markush structures can be described for compounds with substituents at several
positions, and often many thousands
of possible compounds are deÜned in
this way. An important part of chemical database searching is the ability
to Ünd possible Markush structures
to rule out priority in the patent application. Chemical drawing programs 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 *presumptive test that gives a variety of
colour changes with a range of compounds. It is particularly useful for
detecting opiate alkaloids and for
amphetamines and methamphetamine. Marquis reagent is a mixture
of methanal (formaldehyde) solution
in water with sulphuric acid. Mescaline gives an orange colouration.
With morphine, a violet colour is
produced. Amphetamines give an orange-red colour and methamphetamine gives an orange colour. The two
can be distinguished by the *Simon
test. The mechanism involves attack
of the aldehyde an a substituted aromatic ring to form a carbocation. Further reaction forms a coloured dimer
of the original molecule.
marsh gas Methane formed by rotting vegetation in marshes.
Marsh’s test A chemical test for arsenic in which hydrochloric acid and
zinc are added to the sample, arsine
being produced by the nascent hydrogen generated. Gas from the sample is led through a heated glass tube
and, if arsine is present, it decomposes to give a brown deposit of
arsenic metal. The arsenic is distinguished from antimony (which gives
a similar result) by the fact that antimony does not dissolve in sodium
chlorate(I) (hypochlorite). The test
was devised in 1836 by the British
chemist James Marsh (1789–1846).
martensite A solid solution of carbon 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.
mascagnite A 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).
mass A measure of a body’s inertia,
i.e. its resistance to acceleration. According 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 experience 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 enables 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 measured in terms of this standard.
The body used for this purpose is a
1-kg cylinder of platinum–iridium
alloy, called the international standard of mass.
mass action The law of mass action 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 reactant is taken to be its molar concentration. For example, for a
reaction
xA + yB → products
343
mass action
m
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actually been synthesized. In 1925
The US Patent OfÜce ruled that such
patents were valid. Markush structures can be described for compounds with substituents at several
positions, and often many thousands
of possible compounds are deÜned in
this way. An important part of chemical database searching is the ability
to Ünd possible Markush structures
to rule out priority in the patent application. Chemical drawing programs 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 *presumptive test that gives a variety of
colour changes with a range of compounds. It is particularly useful for
detecting opiate alkaloids and for
amphetamines and methamphetamine. Marquis reagent is a mixture
of methanal (formaldehyde) solution
in water with sulphuric acid. Mescaline gives an orange colouration.
With morphine, a violet colour is
produced. Amphetamines give an orange-red colour and methamphetamine gives an orange colour. The two
can be distinguished by the *Simon
test. The mechanism involves attack
of the aldehyde an a substituted aromatic ring to form a carbocation. Further reaction forms a coloured dimer
of the original molecule.
marsh gas Methane formed by rotting vegetation in marshes.
Marsh’s test A chemical test for arsenic in which hydrochloric acid and
zinc are added to the sample, arsine
being produced by the nascent hydrogen generated. Gas from the sample is led through a heated glass tube
and, if arsine is present, it decomposes to give a brown deposit of
arsenic metal. The arsenic is distinguished from antimony (which gives
a similar result) by the fact that antimony does not dissolve in sodium
chlorate(I) (hypochlorite). The test
was devised in 1836 by the British
chemist James Marsh (1789–1846).
martensite A solid solution of carbon 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.
mascagnite A 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).
mass A measure of a body’s inertia,
i.e. its resistance to acceleration. According 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 experience 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 enables 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 measured in terms of this standard.
The body used for this purpose is a
1-kg cylinder of platinum–iridium
alloy, called the international standard of mass.
mass action The law of mass action 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 reactant is taken to be its molar concentration. For example, for a
reaction
xA + yB → products
343
mass action
m
www.AzShimi.ir www.AzShimi.com