212 
The N.Z. Journal of Science and Technology. 
[May 
A known weight (about 3 grammes) of dry material is heated with 10 c.c. of 
this acid in a porcelain dish on a wire-gauze mat over a small Bunsen flame 
until thick fumes are evolved. After cooling, water is added, and the 
residue filtered off, washed, dried, and weighed. 
This method was adopted after trial of details given by different 
authors as giving the most satisfactory results with the local clays. 
An examination of the scheme of analysis shows that the composition 
of a clay is stated in such a way that it suggests to the manufacturer the 
means of modifying that composition. A modification of the table gives 
the following:— 
A, “ clay fraction ” 
B, “ sand fraction ” 
(Actual clay 
j Fine sand, &c. 
[Fine carbonates, &c.-— i.e., flux 
(Coarse sand, &c. 
(Coarse carbonates, &c. .. 
{d) 
(«) 
(b) 
(«) 
(/) 
These fractions, A and B, are the easiest into which to divided a clay 
by allowing it to settle in a pond, and their relative proportions can be 
controlled in practice. Suppose, for example, that the clay gave trouble 
by “ boiling out ” or slagging, and the analysis showed that iron or 
carbonate of lime was particularly abundant in the coarser fraction, the 
latter could be settled out from a slow stream of clay slurry. A non¬ 
fluxing sand could then be added to the purified material. Similarly, 
variation of composition might be accurately adjusted by the admixture 
of other clays, sands, or “ grogs ” of determined composition. 
Results of Examination of a Number of Auckland Clays. 
Definitions .—The general terms “ clay ” and “ natural clay ” are used 
exclusively for the mixtures of more or less plastic material as they occur 
in the natural deposits. The terms “ clay fraction ” and “ sand fraction ” 
are used exclusively for the elutriation fractions as given in A and B above. 
For the chemically pure material ( d ) above as purified in the analytical 
process the term “ actual clay ” is used. 
Single experiments only are recorded, but the results were in all cases 
confirmed by duplicate. When several determinations did not agree 
within 2 per cent, the average of the results was taken. 
KAOLIN FROM MAUNGAKAKARAMEA. 
In the wall of one of the numerous fissures on the northern spurs of 
Maungakakaramea, the Rainbow Mountain of the Waiotapu district, the 
author discovered a band of much-altered rhyolite which in places was 
continuous with pockets of a white plastic clay. This was probably the 
product of local solfataric action, as there are still steam-vents and hot 
springs on the mountain itself. By combined analysis it was found to 
be at least 99 per cent, actual clay. 
An ultimate analysis by fusion with alkali carbonates was found to 
give the composition of a pure kaolin. To be quite certain that the 
kaolin composition was not due to an accidental compensation of minerals 
the homogeneity of the material was tested as follows : A sample of the 
clay was suspended in a beaker of water and separated into two approxi¬ 
mate halves by the rate of settling. The result of the ultimate analyses 
of these two fractions is stated in Table I. It is seen that the composition 
of the two fractions is approximately the same. 
