BULLETIN OF THE BUSSEY INSTITUTION, 23 
suggested above, have probably been deprived of lime by chemical 
action. It is of interest to note that the proportion of magnesia in 
the samples analyzed is commonly unusually large where the amount 
of lime is small, as it naturally would be in case a mud containing 
calcareous casts or shells had been exposed to the solvent action of 
weak chemical agents, such as would dissolve carbonate of lime rather 
than carbonate of magnesia. 
The Pacific muds were all highly siliceous, as will be seen from the 
table of analyses. No perceptible bubbles of carbonic acid were 
given off from either of them on the addition of muriatic acid. 
Most of them contained small quantities of manganese. The varia- 
tions in the amounts of potash and phosphoric acid found in the 
different samples of muds are noteworthy. 
I have to thank my assistant, Mr. J. Andrew Henshaw, for much 
of the analytical work upon the rocks and muds above enumerated, 
and to testify to the great care and assiduity with which he has con- 
ducted the work. 
The methods of analyses employed in most instances for the rocks 
were as follows: — 
Potash was estimated by the method of Professor J. Lawrence Smith, 
familiar to American analysts. 
To estimate phosphoric acid, eight grammes,* or thereabouts, of the 
finely powdered rock were heated in a platinum crucible together with 
four or five times as much carbonate of soda, that had been proved to be 
absolutely free from any contamination of phosphate, until the entire 
mass was in a state of calm liquid fusion. 
The fusion was commonly effected without difficulty by means of 
powerful gas-burners or with an alcoholic blast-lamp (eolipile). A few 
of the specimens were so refractory as to resist in some degree the fusion 
by means of lamps, but these exceptional rocks were quickly reduced by 
the following method, which I would commend to analysts as a neat and 
effective process: The platinum crucible which contains the reck and 
flux is fitted to a triangle of iron wire guarded with bits of pipe-stem. 
By bending the long wires which form its three points, this triangle is 
hung from the rim of a small Hessian crucible, from which the bottom 
has been knocked off, in such wise that the loaded platinum crucible 
may rest on the triangle within and at the centre of the Hessian crucible 
without touching the latter at any point. The small Hessian cruci- 
* In some instances, where the amount of phosphoric acid was supposed to be 
small, quantities of the rock very much larger than eight grammes were fused 
as above described ; but there was no advantage in using these larger quantities, 
and the fusing of them was inconvenient and troublesome. 
