INJURIOUS EFFECTS OF TAR ON CORDAGE. 25 
From these results M. Duhamel concludes : 
1. That untarred cordage in constant service is one third more durable 
than the same cordage when tarred. 
_ 2. That untarred cordage retains its strength for 2 much longer time when 
it is kept in store. 
3. That untarred cordage resists the ordinary injuries of the weather one 
fourth longer than when it is tarred. 
_ These results of direct experiments have been confirmed by the observa- 
tions of seamen; but they have invariably found, that untarred cordage is 
weaker than tarred cordage, when it is exposed to be alternately wet and 
dry; that tarred cordage is chiefly useful for cables and ground tackle, 
which must be constantly soaked in water; and that cordage, superficially 
tarred, is always stronger than what is thoroughly tarred, and resists better 
the alternate conditions of dryness and wetness. 
Several important experiments on the relative strengh of tarred and un- 
tarred ropes were made by Mr W. Chapman,} chiefly with the view of deter- 
mining the effects of his method of preserving ropes with purified or washed 
tar. Three pieces of rope were made on the 10th of August, 1808, of 12 
threads in each strand. The first was an untarred rope, the second a rope 
made of washed tarred yarn, and the third a common tarred rope. A part 
of each of these ropes had their strength tried on the breaking machine ; and 
another part was steeped in water for about three months, and then taken to 
a foundry stove, which is supposed to have been at about 130° of Fahrenheit. 
They remained in the stove about three months. After that they lay at Mr. 
Chapman’s ropery till Nov. 3d, 1803, when the following experiments were 
made with them: 
‘When made. Portion of 
ae 10th, | Nov. 3d, 1803.Joriginal Strength 
802. retained. 
Cwt. Cut. Cwt 
White rope . ... . 33-4 19 577.8 
Common tarred rope . . 22-2 7:35 33:0 + 3 
Washed tarred rope . . 2971 12:35 43°38} 5 
The tarred ropes were both brittle; but the latter was more so, and they 
both cracked on bending." 
[Mr. Chapman has also observed that though cordage is injured by 
tarring in cold climates, it is much more rapidly so in hot climates. ] 
The following experiments were made in 1807, by Mr. Chapman, for the 
purpose of showing the injury arising from the retention of that portion of 
the essential oil which cannot be dispensed with, and also the injury which 
arises from the progressive disengagement of the acid of essential oil. 
Weight with which 
Weight with it broke after 
shacks it broke exposure 
when Moist. to a Stove for 
four months. 
Cwt. Cwt. 
Untarred rope. . . . -| . 45°75 38:97 
Rope tarred with cold tar . 51:29 26°40 
Ditto with boiled tar. 38°94 25:07 
1 Author of ‘Treatise on the progressive endeavours to improve the Manufacture 
and Duration of Cordage ;’ London, 1808. 
