243 
Tuer Trenactry oF GELATINE. 
[Publication No. 35.] 
By ARTHUR L. FOLEY. 
Some years ago the author called attention to the fact that the co- 
hesive forces of gelatine must be considerably greater than those of glass 
in order that a single drop of gelatine in drying and contracting on a glass 
plate may pull a ring or disk of glass from the plate." The forces here 
exhibited are apparently greater than shown in the common, though not 
well known, process of producing chipped glass by flowing a pane of glass 
with gelatine and allowing the gelatine to dry. Inasmuch as the author 
could not find in any of the literature at hand any recorded values of the 
tensile strength of gelatine, he requested one of his students to attempt 
to determine its value. Several plans were tried, the one giving the best 
results being as follows: 
Gelatine threads were drawn out between the ends of small wooden 
sticks (about the size of a match) after dipping one end of each in melted 
gelatine. The diameter of a thread was varied by varying the size and 
temperature of the gelatine drop, the thickness of the fluid, the length 
of the thread and the time spent in drawing it. To the other end of the 
wooden sticks there had been attached previously small wire hooks for 
suspending the upper end of the threads and for attaching a small cloth 
sack to the lower end. Into this sack dust shot were slowly run until the 
thread broke. The cross-section of the thread was then measured at the 
point of break. 
When the section of a thread was regular its cross-sction was cal- 
culated from the diameters measured by a micrometer microscope. Threads 
of irregular cross-section were placed under a microscope with a camera 
lucida attachment and a tracing made of the perimeter. The area of the 
tracing was measured with a planimeter and the area of the section of 
the thread itself calculated from the known magnifying power of the 
microscope and attachment. 
When glass threads are drawn they are usually almost cylindrical. 
Gelatine threads also are probably approximately cylindrical at the time 
1 Note on the Molecular Forces in Gelatine. Science, Vol. 23, p. 790, May 18, 
1906. 
