160 
MR. RENNIE’S EXPERIMENTS ON THE FRICTION AND 
Appendix to Tables VII. and VIII. 
Table showing the comparative amount of Friction of different Metals under 
an average pressure of from 54.25lbs. to 69.5 5lbs. as calculated from the 
foregoing experiments. 
Description of Metals. 
Average Weight. 
Proportion. 
Weight per Square 
Inch Area. 
Brass on wrought iron 
lbs. 
69.55 
7.312 
lbs. oz. 
11 12.4 
Steel upon steel 
69.55 
6.860 
11 12.5 
Brass upon cast iron 
54.25 
6.745 
8 0.5 
Brass upon steel 
69.55 
6.592 
11 12.5 
Hard brass upon cast iron 
54.25 
6.581 
6 15.9 
Wrought iron on wrought iron. . 
69-55 
6.561 
11 12.5 
Cast iron upon cast iron 
54.25 
6.475 
8 0.5 
Cast iron upon steel 
69-55 
6.393 
11 12.5 
Cast iron upon wrought iron. . . . 
69-55 
6.023 
11 12.5 
Tin upon wrought iron 
69-55 
5.846 
11 12.5 
Brass upon brass 
69-55 
5.764 
11 12.5 
Tin upon cast iron 
54.25 
5.671 
8 0.5 
Steel upon wrought iron 
69.55 
5.198 
11 12.4 
Tin upon tin 
69.55 
3.305 
11 12.5 
Remarks on Tables VII. and VIII. 
1. From the preceding experiments it appears: — that the friction of metals varies with their 
hardness. 
2. That the hard metals have less friction than the soft ones. 
3. That without unguents and within the limits of 32lbs 8oz. per square inch, the friction of hard 
metals against hard metals may very generally be estimated at about one-sixth of the pressure. 
4. That within the limits of their abrasion the friction of metals is nearly alike. 
5. That from 1.66cwt. per square inch to upwards of Gcwt. per square inch, the resistance increases 
in a very considerable ratio, being the greatest with steel on cast iron, and the least with brass on 
wrought iron, their limits being as 30, 36, 38, and 44cwt. An experiment was made with a weight 
of 10 tons per inch on hardened steel, which abraded. 
The remarkable property of steel in hardening, and its power to resist abrasion, render it preferable 
to every other substance yet discovered in reducing the friction of delicate instruments, as is exem- 
plified in the different experiments on the pendulum, and the assay and other balances recently in- 
troduced at Ilis Majesty’s Mint and the Bank of England. 
The experiments of Messrs. Cavendish and Hatchett in the years 1798 and 1801 at His Ma- 
jesty’s Mint on the alloys, specific gravity, arid comparative wear of gold coin by friction, likewise 
prove that friction and abrasion were less in the hard than soft metals. Philosophical Transactions 
for 1803, Part I. 
