I was reading this and curious about whether the 'liquid to...

I was reading this and curious about whether the 'liquid to solid' would actually work at all. Surely it would not matter at all if something is liquid or solid its mass would remain constant - you can't create mass out of nothing! Also assuming it's contained within a solid container it's displacement of water or volume would therefore make no difference whatsoever. If it's contained within a flexible surface them perhaps it would, but If it's displacement of water remains the same, and it's total mass is the same then it will displace the same volume of water and so this change to liquid won't make it float or sink.