Empirical formula for Ca 40.078 22.3%
As 74.9216 41.6%
O 15.9994 35.6%
H 1.00794 0.560%

The empirical formula : CaAsO₄H

Further explanation  

The empirical formula is the smallest comparison of atoms of compound =mole ratio of the components

The principle of determining empirical formula

Determine the mass ratio of the constituent elements of the compound.   Determine the mole ratio by by dividing the percentage by the atomic mass Ca

As

O

H

Divide by the smallest ratio(0.555) :

Ca : As : O : H ⇒

The mass has escaped into a gas which you can not see so the law stays true.

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