I found a recipe for blackcurrant jelly (not gelatin jelly, jam jelly) in the book, p1100, and thought I would try it out. I did look up other references to get a general feel for this jam too, notably "Preserves" by Pam Corbin and the Historical Foods website (which I love by the way, it's a fab site).
I melded these together to come up with a final method that was mix of all three.
The one suggestion I'd make to anyone planning an attempt with this recipe, is to ignore the timings suggested by (any version of) this book. I used a thermometer as well but doubt their reliability. Either way, I've come to the conclusion that Mrs Beeton my have favoured rock hard jams, more suited to cutting diamonds or breaking windows than slathering over hot toast. Go easy on the boiling and keep a supply of frozen saucers handy.
First I washed and de-stemmed a pound (lb) of blackcurrants, then put them in my largest saucepan with a quarter of a pint of cold water. I brought this up to a gentle simmer and cooked for 10 minutes.
I then added 3/4 lb sugar and very gently simmered this mix for half an hour, stirring very frequently as it really does want to stick to the pan quite a lot.
Finally, after the half an hour, I kicked up the heat and brought the mixture to a boil for several minutes.
My thermometer never hit 104 degrees, but I started to get suspicious when I could see the jam flaking off the wooden spoon. I dolloped some onto a cold plate from the freezer and lo and behold, it set rock solid in a few seconds flat.
I now suspect that it's practically ready after that half an hour's simmer so, if you do make this, be vigilant as it's an easy one to over-set. Saying that, it tastes wonderful even if you do, so all is not lost!