| Reference | Method; T, K | Ionic strength (M) | [Ho3+] | log β1,H |
| 5 | P; 298 | 0.3 M NaClO4 + 0.02 M Ba(OH)2 | [0.004 - 0.009 M] Ho(ClO4)3 | −9.96 |
| 6 | SE; 298 | 0.1 M LiClO4 | [10−7 M] | −5.7 |
| 7 Present work Present work | SP; 298 SP, P 303 SP, P 303 | 0 M 2 M NaClO4 2 M NaCl | [0 - 0.00008 M] HoCl3 2.5 × 10−4 M PrCl3 2.5 × 10−4 M PrCl3 | −8.15 ± 0.15 −8.01 ± 0.05 −8.16 ± 0.02 |