CONCLUDING REMARKS. 175 



plexity and uncertainty in perfecting the invention. After 

 this cause of the failure of many experiments was detected and 

 guarded against, when it became desirable to vulcanize speci- 

 mens of any considerable thickness, or from -g-'j to y'g- of an 

 inch in thickness, they were found to be blistered in nearly 

 every instance ; and afterwards, when the manufacture of the 

 goods was established, this defect rendered the goods so im- 

 perfect and unmerchantable, and occasioned so great losses, 

 as almost to induce some of the manufacturers to abandon the 

 business altogether. The causes of this effect also were not all 

 known, and some of them were not even suspected for a long 

 time. They were so numerous that it is no way surprising 

 that it could not then be told to which of them might be attrib- 

 nled the failure of any particular experiment, or that it should 

 then, in ignorance of them, be impossible to guard against them 

 all at any one time. Another circumstance that served to 

 mislead the inventor and subsequently the manufacturers, was 

 the shortness of the time required to heat or vulcanize thin 

 coats of gum, being only a few minutes, while it was not then 

 known that it required the heat to be gradually raised several 

 hours to vulcanize perfectly thicker coats of gum, or only yW 

 parts of an inch and more, without blistering. 



Blistering occurs when the gum is dissolved with turpentine 

 under the following circumstances : 



1st. When the turpentine is old or acidulated. 



2d. When the sulphur is acid, as it is usually found in the 

 market. 



3d. When the white lead, gum or other ingredients, are acci- 

 dentally or otherwise mixed with substances that generate gases 

 of any kind in the fabrics while they are being heated. 



4th. When any of the ingredients of the compound are wet 

 when mixed, so that they generate steam in heating. 



5th, When the turpentine is not well dried off before the 

 fabrics are vulcanized. 



6th. The fabrics are also liable to blister when solvents are 

 not used, if a high degree of heat is applied too suddenly, or if 



-S!^2'> 



