give more on saltpeter could to much kill you can you find it in your blood?

Answer 1

too much of any thing, sugar, salt, pepper can cause harm to anybody.

Answer 2

We seem to be able to tolerate a small amount of it because sodium nitrate and potassium nitrate are both used to preserve meats.

I am not aware of the corresponding blood levels for the intakes given below and I suspect that they will vary with the size of the patient, body habitus, co-ingestants, kidney disease, etc.

Potassium nitrate
Estimate of acceptable daily intakes for man

mg/kg body-weight

Unconditional acceptance 0-0.4
Conditional acceptance 0.4-0.8

Sodium nitrate
Poisoning in man may result from a total oral daily dose in excess of 4 g or from a single dose of more than 1 g. 8 g may be fatal and 13-15 g are generally fatal.

See the sites in wikipedia and JECFA - Joint Expert Committee on Food Additives