On Spontaneous Inflammations . 21$ 
heat produced depends on several circumstances, and va- 
ries chiefly in the ratio of the duration of the friction, and 
of the nature and surface of the rubbed bodies. If the 
friction takes place between combustible bodies, such as 
wood, the heat it excites may often be sufficient to in- 
flame it ; if the bodies are not combustible, such as stones, 
or little combustible, as metals, they do not inflame them- 
selves ; but they may communicate to other combustible 
bodies around them such a degree of heat that the latter 
will inflame by contact with the atmospheric air. 
D. Palcani repeated the experiments long known for 
obtaining fire by the friction of two pieces of wood, giv- 
ing to one of the rubbing pieces the form of a tablet, and 
to the other that of a spindle or cylinder : the result of 
some of these experiments will be sufficient to show, that, 
in the construction of machines and instruments, more 
attention ought to be paid to the choice of the wood des- 
tined to be exposed to mutual friction. 
Cylinders. Tablet. Duration. Effect. 
Box wood - - Box - - 5 min. Sensible heat. 
Ditto - - - Poplar - Ditto Ditto 
Ditto - - - Oak - - Ditto Ditto 
Ditto - - - Mulberry 3 - - Considerable heat and 
smoke 
Ditto - - - Laurel - Ditto Ditto 
Laurel « - » Poplar - 2 - - Ditto 
Ditto • - Ivy - - Ditto Ditto 
Ivy - - - - Box - - 3 - - Ditto 
Ditto - • » Walnut - Ditto Ditto 
Olive - - - Olive - - Ditto Ditto 
Mulberry - - Laurel - 2 - „ - Consid. heat, smoke, and 
blackness 
Ash - - - - Oak - - 5 - - Sensible heat 
Ditto ... Fir - - Ditto Ditto 
Pear-tree - - Oak - - Ditto Ditto 
Cherry - - - Elm - - Ditto Ditto 
Plum - - - Apple-tree Ditto Ditto 
Oak — - - - Fir - - Ditto Ditto 
