238 Transactions of the 



films, or nodules, thus obtained easily separate by friction into 

 the same sort of particles. 



To obtain any silica deposition of a structural character, it was 

 thought necessary to place some retarding influence in the way of 

 the precipitation of the mineral from the gaseous combination 

 above mentioned, and for this purpose a mixture of glycerine and 

 water was tried and found to answer. The materials for making 

 the gas, powdered glass, or flint, powdered fluor spar' and sulphuric 

 acid, were shaken up in a small flask supplied with a glass exit- 

 pipe about -i\" in diameter. This apparatus was placed upon a 

 retort stand, so that it was easy to hold an evaporating dish in the 

 right hand and immerse the end of the exit-pipe in the glycerine 

 and water it contained, while the left hand was at liberty to regu- 

 late the heat and rate of formation of the gas by approximating 

 or withdrawing a spirit lamp from beneath the flask, as the case 

 required. A little mercury was placed at the bottom of the evapo- 

 rating dish in order that the end of the exit-pipe might be dipped 

 under its surface, if at any time the deposition of sihca became so 

 rapid as to threaten to stop it up. By allowing the gas to come 

 over at a moderate rate, and letting the tip of the exit-pipe dip just 

 under the surface of the water and glycerine, a number of thin films 

 were quickly formed, some of great tenuity, and others thicker, but 

 all avoiding anything like aggregation into lumps. 



These films were easily taken up by a small sable brush, placed 

 on a glass slide and washed to remove the glycerine, with successive 

 drops and small streams of water. In doing this, care is necessary 

 not to let the water-stream float them away, or create confusion by 

 carrying one film on the top of another. When freed from glycerine 

 the films can be examined in clean water under glass, or allowed to 

 dry perfectly and then mounted in balsam, the latter being the 

 most convenient. A shde thus prepared will probably contain films 

 of difi'erent thicknesses, some perhaps consisting of a single or double 

 layer of beads evenly and closely arranged, and others having more 

 bead layers, and the upper ones either in confused groups or in 

 approximately regular patterns. If the films are in either of the 

 last conditions, transparent illumination with oblique light often 

 exhibits nothing but confusion, and with small pencils of direct 

 hght, obtained with the smaller stops of a condenser, an organic 

 aspect is frequently noticeable, as if a number of dingy bacteria-like, 

 fungoid, or small bodies were growing upon some base. PI, LXIII,, 

 Fig. 1, gi\e3 a good idea of this appearance in the case of a film tend- 

 ing towards a cellular structure. In Fig. 2 the cellular structure is 

 more distinct, as shown in other films. Figs. 3, 4, 5, exhibit simula- 

 tions of organic cell forms, and might be taken for veritable results 

 of secretions and depositions occurring in the processes of organic 

 life, but the cell hollows are referable to the bursting of minute gas- 



