EN
We report the low-temperature specific-heat simulation results and reanalyzed measurement data on polydomain Yb_4As_3 in magnetic fields B = 0 and 6 T. The data considered here are independent and supplement those considered earlier. A quantitative agreement has again been achieved between the magnetic experimental specific-heat data and the numerical results obtained by the quantum transfer-matrix simulation technique, yielding a new evidence in favour of the Heisenberg model of the antiferromagnetic spin S = 1/2 chain with the value of the exchange integral J/k_{B} = - 28 K. The finite-size quantum transfer matrix approximants have been extrapolated exploiting the procedure developed previously. On the basis of the data in magnetic field and using the corresponding density-matrix renormalization group results, the energy-gap size Δ has been estimated for the applied magnetic field B = 6 T, leading to the experimental verification in the extended region of the scaling law Δ ∿ B^{2/3} following from the sine-Gordon model.