An alternative and, perhaps, better way of taking the sample is to withdraw portions at equal intervals from the stream of metal whilst the pot is being emptied; equal weights taken from these portions and mixed (by melting or in some other way) give a fair sample of the whole. In addition, separate assays of each portion will show to what extent the metal lacks uniformity in composition For example, samples taken at the beginning, middle, and end of a run gave the following results in ozs. of silver per ton: 475, 472, 466, showing an average result of 471 ozs. Fifteen fractions taken at regular intervals during the same pouring ranged from 475 ozs. to 464 ozs.: the average result was 469.8 ozs. The same lead cast into bars and sampled by sawing gave an average of 470 ozs.[34] In another case[35] samples drawn at the beginning, middle, and end of a run gave 1345 ozs., 1335 ozs. and 1331 ozs. The mean result in such cases is always a reasonably safe one, but evidently where the metal varies a good deal it is safer to take more than three dips. Imagine such lead run into moulds and allowed to become solid as bars; the difference between bar and bar would not be greater than that between corresponding dip samples. But in each bar the distribution of the silver and gold is very seriously affected during solidification. Chips taken from the same bar of auriferous lead may show in one place 23 ozs. of gold to the ton, in another 39 ozs.; similarly with silver they may vary as much as from 900 ozs. to 1500 ozs. to the ton. This rearrangement of the constituents of a bar takes place whilst the lead is partly solid, partly liquid. The most useful conception of such half-solidified metal is that of a felted spongy mass of skeleton crystals of comparatively pure lead saturated with a still fluid enriched alloy. If the solidification of an ingot of impure tin be watched it will be evident that the frosted appearance of the surface is due to the withdrawal of the fluid portion from a mat of crystals of purer tin which have been for some time solid and a contraction of the mass. The shrinking of the last part to become solid is further shown by the collapse of the surface of the ingot where weakest; that is, a furrow is formed on the flat surface. In other cases of fused metal there is expansion instead of contraction in this final stage of the solidification, and the enriched alloy then causes the upper face of the ingot to bulge outwards. There are other causes effecting the redistribution of the metals through the ingot. There can be no general rule of wide application showing which part of a bar is richest and which poorest in the precious metals. This will depend on the quantities of gold or silver, on the quantities and kinds of other metals present and on the manner of casting. The student is advised to consult Mr. Claudet's paper which has been already referred to.