According to a generally accepted principle, the data describing test
conditions should be always sufficiently complete to enable the reader
to repeat the experiment. However, it is not quite an exception if a
technical report on or a scientific publication of results of grinding
tests carried out in lab-scale tumbling mills omits most relevant dat
a (e.g.: total mass of the mill charge) in favour of less important in
formation (e.g,: number and sizes of the grinding media) or of somewha
t doubtful data (e.g.: volume fraction occupied by the mill charge in
the grinding chamber). Shortcomings of that kind may occur less freque
ntly if the information on the conditions of the grinding tests can be
checked for completeness by referring to relationships which comprise
the main variables of the net power draw of the mill and of the energ
y transferred to the mineral load. In addition, relationships of that
kind would offer the advantage of compressing the information on test
conditions, and of making test results better comparable as well, A ba
sic relationship serving the said purpose is derived from simplified s
imilarity considerations. A nominal coefficient of mill-internal frict
ion is found suitable to normalize the results of net power measuremen
ts. The main free variables of grinding tests are combined in an index
which is proportional to the specific energy consumption.