Magnesium sulfate anhydrous hot pack having an inner bag provided with a perforated seal

Claim 1

In a hot pack for use in providing an increase in temperature from the ambient temperature comprising a group of three pliable sleeve type plastic bags, two of said bags being of approximately the same size and strength forming the exterior and contiguous interior major liners of the pack, an inner bag comprising a minor liner being formed as a sleeve type bag and having dimensions and strength substantially less than the combined major liners enveloping said inner bag, the upper marginal seams of said major and minor liners being co-extensive and sealed together to form the upper end of the pack, the lower end the minor liner having a closing seam being capable of pressure rupture upon application of manual force, said inner bag having a seal extending below the upper marginal seams, the improvement which consists of a perforation provided through said inner bag within the seal provided below the upper marginal seams to provide a pressure relief at the time of activation of the pack to prevent the pressure from acting against the upper marginal seams and thereby cause rupture of the pack proximate said seams, the inner bag disposed for holding a quantity of water, the interior major liner disposed for holding a quantity of magnesium sulfate anhydrous which upon reaction with said water provides for an increase in temperature, the ratio by volume of the magnesium sulfate anhydrous to water being between about a 1 to 1 ratio to a 1 to 2 ratio.