Curious Hollow Glass Cube

Found this interesting curiosity at a junk/thrift market and being an avid glass collector had to have it. It measures aprox. 6x6 and although hollow is heavy. Here's what I think - my cube was used to transport something that absolutely needed to remain dry, salt perhaps, because there is a glass plug for a tight seal and another small hole created by a hot tool to empty the content out whenever it reached its destination.
There are no cracks or breaks. It's extremely sturdy, made to last!
I would love to know for sure what its use was but even if I never find out I still think it's wonderful!
Any suggestions anybody?