_Securing Calotype Negatives._--Will any of your correspondents be good
enough to say what they consider the best method of securing a calotype
paper negative for a few days or a week, in cases where it may be
difficult, from lack of conveniences during that time, to use hyposulph.,
with its consequent washings, &c.? Some, I believe, recommend bromide of
potassium; some, the iodide; others, common salt: but I should like to know
which is considered the _best_; what strength, and how applied. Also,
whether any subsequent treatment is necessary previous to the final
application of the hypo.