▁attra ctions , ▁consequ ently ▁hyd r ates ▁are ▁common ▁for ▁sal ts ▁that ▁contain ▁+ 2 ▁and ▁+ 3 ▁c ations ▁as ▁well ▁as ▁− 2 ▁an ions . ▁ ▁In ▁some ▁cases , ▁the ▁majority ▁of ▁the ▁weight ▁of ▁a ▁comp ound ▁ar ises ▁from ▁water . ▁ ▁Gla uber ' s ▁salt , ▁Na 2 SO 4 ( H 2 O ) 1 0 , ▁is ▁a ▁white ▁cry st all ine ▁solid ▁with ▁ ▁greater ▁than ▁ 5 0 % ▁water ▁by ▁weight . ▁ ▁Consider ▁the ▁case ▁of ▁nick el ( II ) ▁ch lor ide ▁hex ah yd rate . ▁ ▁This ▁species ▁has ▁the ▁formula ▁Ni Cl 2 ( H 2 O ) 6 . ▁ ▁Cry stal log raph ic ▁analysis ▁reve als ▁that ▁the ▁solid ▁consists ▁of ▁[ trans - N i Cl 2 ( H 2 O ) 4 ] ▁sub un its ▁that ▁are ▁hydro gen ▁bond ed ▁to ▁each ▁other ▁as ▁well ▁as ▁two ▁additional ▁mole cules ▁of ▁H 2 O . ▁ ▁Thus ▁ 1 / 3 ▁of ▁the ▁water ▁mole cules ▁in ▁the ▁cry stal ▁are ▁not ▁directly ▁bond ed ▁to ▁Ni 2 + , ▁and ▁these ▁might ▁be ▁term ed ▁" water ▁of ▁cry st all ization ". ▁ ▁Analysis ▁The ▁water ▁content ▁of ▁most ▁comp ounds ▁can ▁be ▁determined ▁with ▁a ▁knowledge ▁of ▁its ▁formula . ▁ ▁An ▁unknown ▁sample ▁can ▁be ▁determined ▁through ▁therm og rav imet ric ▁analysis ▁( T GA ) ▁where ▁the ▁sample