Cures - help please

[sausagedevil]

Hi, I'm quite new to fermented sausage making and have been trying to soak up as much information as i can about the process but am finding that the more i find out the less i know.
Can anyone help with a cure#2 question.
I have bought cure#2 from sausagemaking.org and it contains sodium nitrite and sodium nitrate and salt.
I have noticed some recipes call for cure#2 or saltpetre. Are these interchangeable as long as the correct amounts of salt are added???
Saltpetre is potassium nitrate i believe so is it the nitrate part of the chemical that is important rather than the sodium or potassium part???
I have bought a product from a butchers wholesaler that was sold to me for either dry curing or brining to make bacon. This contains salt, sugar, sodium nitrite and potassium nitrate. It is sold in 10kg buckets and i am wondering if this is suitable as a replacement for cure#2 and salt in my fermented sausage recipes????
Any ideas???
Pablo.

[the chorizo kid]

it's the nitrate/nitrite part not the sodium or potassium.
cure #2 is used at about 1/5 tsp per pound of meat. this is such a small amount that only a purist would account for the salt portion in the cure #2 in terms of the overall salt/pound. [if a sausage calls for 1 1/2 tsp salt per pound, i would use this, even if my 1/5 tsp cure #2 has some salt in it]. in other words, add cure, then add whatever amount of salt is called for.
although chemically the saltpetre is similar but not identical to cure #2 [an expert may answer this better], i do not believe they are equivalent. therefore, i would not simply substitute saltpetre, gram for gram, when cure #2 is called for. they are different enough that you should follow the recipe; not make substitutions. ie 1/5 tsp saltpetre is not the same as 1/5 tsp cure #2.