The alcohol used for burning purposes in the United Kingdom is mineralised methylated spirit, which, at a strength of 62° over proof,1 may be taken as containing on an average: -

Per cent. by volume.

Ethyl alcohol ................................................

83.1

Methyl „ ................................................

7.7

Acetone, esters, etc. ......................................

1.2

Mineral naphtha ...........................................

0.4

Without sensible error the last two items may be grouped together as acetone, 16 per cent., for calculating the calorific value. Expressed as percentages by weight, the composition of mineralised methylated spirit is then: -

1 Somewhat stronger spirit is obtainable, up to 64° or 65° over proof (sp. gr. 0.8214 to 0.8193).

Per cent. by weight.

In 1 gram.

Ethyl alcohol ...................................................

79.9

0.799

Methyl ,, ...................................................

7.4

0.074

Acetone, etc. .................................................

1.5

0015

Water ....................................................

11.2

0.112

100.0

1.000

Multiplying by the corresponding higher calorific values as already given, we have: -

0.799

X

7,237.8

-

5,783.2

calories.

0.074

X

5,212.5

=

385.7

"

0.015

X

7,486.5

=

112.3

"

.. the higher calorific value of mineralised methylated spirit

=

6,281.2

"

This is equal to 11,306 British heat units (B.Th.U.).

To find the lower or "net " calorific value, we calculate the lower values, as already explained, for absolute ethyl and methyl alcohols and acetone: the results are 6,603.7.. 4,5637, and 6,9830, respectively. Then: -

0.799

X

6,603.7

=

5,276.4

0.074

X

4,563.7

=

337.7

0.015

X

6,9830

=

104.7

Deduct for the water present 0.112

X

537

=

5,718.8 60.1

.*. Lower value

= 5,658.7 gram-calories, or 10,185 British thermal units