362 



GOODYEAR ON GUM-ELASTIC. 



are inflated with air, some remarks upon the buoyancy of dif- 

 ferent articles may here be made. 



It is generally supposed, at any rate it is the first impression 

 of most minds, and even of a great portion of those who are 

 well educated, that in order that an article may be sufficiently 

 buoyant to answer the purpose of a life-preserver, it must be in- 

 flated with air, and must be so tight that the air cannot escape ; 

 whereas if the sides of the article are kept distended, it may be 

 very leaky, and it will yet be a great length of time before it will 

 become unsafe, when otherwise it would collapse and allow the 

 wearer to sink instantly, if the sides were not kept distended by 

 some resistance greater than the pressure of the water without. 



The force of these remarks may be illustrated by a barrel 

 with the bung out, or a demijohn with the cork out, both of 

 which it is extremely difficult to sink in the water when they 

 are empty, even when it is intended to do so. In most cases 

 these articles will be quite safe as life-preservers, even if the 

 article is not perfectly tight ; in other words, a small leak, that 

 would cause an article inflated with air to collapse and sink 

 immediately, will not affect the safety of these articles in the 

 slightest degree.* 



The weight that Avill be sustained in the water by any of 

 the articles hereafter described, may be certainly known by its 

 cubic measurement, allowing sixty pounds to the cubic foot, and 

 deducting the weight of the article ; that is to say, a trunk or 

 valise weighing ten pounds, and measuring two cubic feet, will 

 sustain an extra weight of one hundred and ten pounds in the 

 water. 



It is well known that the specific gravity of the human body 

 is less than that of water, and that it will not sink by its own 

 weight, but it requires a buoyant power Avhich is equal, for 

 the average of persons, to about nine pounds. In other words, 

 any article that will keep afloat a lead weight of nine pounds, 

 will sustain a person in such a position in the water that he 

 will be safe from drowning ; but to make u more liberal allow- 



* See Reports, Chapter , page 



J 



