By means of this rule, we may find what increase of heat any proportion of hard corns will occasion, as will be seen in the following table.
| Proportions of hard corns | 1/4 | 1/6 | 1/8 | 1/16 | 1/32 | of the grist |
| Greater heat of the mash | 4° | 3 | 2 | 1 | 1/2 | degrees. |
But the brewing of such malt ought to be avoided as much as possible, as the hard parts afford no strength to the extract.
If a grist is not well and thoroughly mashed, the heat not being uniformly distributed in the different parts of the extract, the liquor of the thermometer, when placed in the running stream of the tap, will fluctuate, and, at different times, shew different degrees of heat. In this case, the best way is to take the mean of several observations, and to estimate that to be the true heat of the mash.
If the gauges of the coppers are not exactly taken, a variation must be expected.
Though the small and hourly variations in the state of the atmosphere have but little influence upon our numbers, a difference will be observed in any considerable and sudden changes either of the heat or of the weight of the air. Our instruments, and in particular the thermometer, are supposed to be well constructed and graduated. If the water cooled in with is more or less hot than estimated, or if the time of mashing or standing is either more or less than was allowed for, the computation must be found to vary from the event.
While the malt is new, if the fire it has received from the kiln has not sufficiently spent itself, this additional heat is not easily accounted for. This is likewise the case, when malt is laid against the hot brickwork of coppers; and, on the contrary, a loss of dryness may be occasioned, if the store rooms are damp.
The artist should be attentive to all these incidents; the not pointing them out might appear neglectful; enumerating more would exceed the bounds of use.
Small grists brewed in large utensils lose their heats more readily, by laying thin, and greatly exposed to the air; and, on the contrary, a less allowance, for the loss of heat, is required in large grists, and to which the utensils are in proportion.