the multi - endothermic salts contemplated for use in the present invention can be added in the afore - described amounts to the total cigarette blend or its individual components . preferably these salts are added to the fastest burning components of the cigarette tobacco blend , generally , reconstituted tobacco or burley tobacco . the effect of reducing blend burn rate is larger when the treatment is applied to these faster burning components . a preferred embodiment of the present invention involves the use of natural tobacco blends containing from about 15 percent to a maximum of about 30 percent by weight of the total blend of at least one tobacco selected from the group of burley and reconstituted tobaccos . most preferably the invention contemplates the application of hydrated magnesium chloride to the reconstituted portion of a blend of natural cigarette smoking tobaccos wherein said reconstituted tobacco is present in an amount of from about 15 percent to a maximum of about 30 percent by weight of the total blend . while burley and reconstituted tobaccos are the fastest burning components of cigarette smoking tobacco compositions the remaining slower burning portions of the blend generally comprise the various varieties of virginia , maryland and oriental tobaccos . the invention is illustrated more explicitly by the following examples . the reconstituted tobacco portion of a typical filter cigarette blend was sprayed with a solution of mgcl 2 . 6h 2 o in an amount such that in the total blend the level of magnesium chloride , as mgcl 2 , was 0 . 67 %, 0 . 90 % and 1 . 64 % of the weight of the tobacco at equilibrium moisture plus the magnesium chloride . the reconstituted tobacco containing the magnesium chloride additive was commingled with the other tobacco components of the blend so as to be distributed substantially uniformly therewith . the blend was made into 85 mm cigarettes with 20 mm cellulose acetate filters using an intermediate porosity paper ( greiner 20 sec .) and the cigarettes were smoked according to standard analytical procedures wherein the cigarettes were smoked with 35 cc , 2 second puffs taken once a minute to a butt length of tipping plus 3 mm . the burn rate and the analytical data for the cigarettes tested are summarized in table 1 . in this and in succeeding tables lbr abbreviates linear burn rate , mbr abbreviates mass burn rate , nfds abbreviates nicotine - free dry solids , hcn abbreviates hydrocyanic acid , ald abbreviates total aldehydes expressed as equivalent ug of acetaldehyde ( ref . p . f . collins , n . m . sarji and j . f . williams , beitrage zur tabakforschung , 7 , 73 - 78 ( 1973 ), and μg stands for microgram : table i______________________________________mgcl . sub . 2 (%) 0 0 . 67 0 . 90 1 . 64 # puffs 8 . 0 8 . 3 8 . 3 8 . 9lbr 5 . 49 5 . 30 5 . 26 4 . 85mbr 64 . 7 63 . 9 62 . 6 57 . 6yields / cignic ( mg ) 1 . 15 1 . 17 1 . 10 1 . 14nfds ( mg ) 15 . 5 15 . 5 15 . 9 16 . 9yields / puffhcn ( μg ) 26 29 . 2 30 . 4 31 . 7tot . ald . ( μg ) 152 142 141 116ph of smoke 6 . 00 5 . 90 5 . 90 5 . 90______________________________________ the data in the foregoing table demonstrate that at each level of magnesium chloride there was a marked decrease in burn rate , whether in terms of puff number , linear burn rate or mass burn rate . there were marginal decreases in smoke ph and total aldehydes and increases in nicotine - free dry solids ( nfds ) and hcn , although the changes were beyond experimental error only for the highest level of the additive . additional burn rate tests were made with 85 mm cigarettes with 20 mm cellulose acetate filters which had been fabricated from a different filter blend of tobacco components and where the levels of hydrated magnesium chloride additive were different from the levels employed in connection with the test summarized in table i . hydrated magnesium chloride was again applied to the reconstituted tobacco portion of the blend . the cigarettes were made with two types of paper , namely , an intermediate porosity paper ( greiner 20 sec .) and a porous paper ( greiner 12 sec .). the cigarettes were smoked according to the aforesaid standard analytical procedures and the test results are summarized in tables ii and iii which follow : table ii______________________________________ intermediate porosity paper______________________________________mgcl . sub . 2 (%) -- 0 . 36 0 . 85 0 . 95ca ( oh ). sub . 2 (%) -- -- -- 0 . 75 # puffs 7 . 7 7 . 9 8 . 2 8 . 0lbr ( mm / min ) 5 . 52 5 . 33 5 . 16 5 . 28mbr ( mg / min ) 61 . 8 60 . 3 57 . 8 58 . 4yields / cignic ( mg ) 1 . 11 1 . 31 1 . 28 1 . 11nfds ( mg ) 17 . 4 18 . 1 18 . 6 16 . 8yields / puffhcn ( μg ) 32 . 5 33 . 6 35 . 9 31 . 1tot . ald . ( μg ) 159 153 134 138ph of smoke 5 . 86 5 . 97 5 . 83 6 . 20______________________________________ table iii______________________________________ porous paper______________________________________ # puffs 7 . 3 7 . 6 7 . 8 7 . 7lbr 6 . 29 6 . 03 5 . 62 5 . 69mbr 70 . 6 67 . 2 63 . 1 63 . 3yields / cignic . ( mg ) 0 . 98 1 . 10 1 . 13 1 . 02nfds ( mg ) 15 . 3 16 . 2 16 . 2 15 . 7yields / puffhcn ( μg ) 31 . 2 31 . 7 35 . 4 32 . 5tot . ald . ( μg ) 158 152 138 152ph of smoke 5 . 84 5 . 94 5 . 87 6 . 26______________________________________ tables ii and iii again demonstrated the marked decrease in burn rate with increasing levels of the hydrated magnesium chloride additive . the yields of smoke components again exhibited marginal changes as in table i , except that nicotine now also showed an increase and smoke ph did not reflect an additive effect . as is evident from the foregoing data , the presence of the magnesium chloride additive tends in some cases to have an effect on smoke component yields . although the changes are very modest , of the order of the experimental error in the analytical procedure employed , and thus are not of much practical significance , further experimental work showed that the variations in smoke components could be negated by the addition of alkaline materials , such as calcium hydroxide , to the total tobacco blend to increase the ph of the tobacco materials . any physiologically acceptable alkaline material , including magnesium hydroxide , basic phosphates and the like , can be employed . calcium hydroxide is preferred because calcium hydroxide does not introduce new elements into the tobacco product . the amount of alkaline material sufficient for this purpose is in the range of about 0 . 1 to about 2 weight percent , and preferably is from about 0 . 5 to about 1 percent . table iv , which follows , illustrates the use of various salts which exhibit analogous endothermic phenomena and in each case the burn rate of the cigarette tobacco blend was substantially reduced . in each instance the blend that was used was similar to that used in the tests hereinabove mentioned and by application of the additive in the form of an aqueous solution to the reconstituted tobacco component of the blend . table iv______________________________________summary of data for various additives lbr mbradditive level (%) # puffs ( mm / min ) ( mg / min ) ______________________________________control 0 8 . 3 5 . 18 64 . 5fenh . sub . 4 cit 0 . 81 8 . 4 4 . 95 61 . 9fecl . sub . 2 . 6h . sub . 2 o 2 . 11 9 . 1 4 . 48 55 . 8fe . sub . 2 ( so . sub . 4 ) . 9h . sub . 2 o 2 . 43 8 . 5 4 . 98 62 . 8mghcit 1 . 67 8 . 3 5 . 03 62 . 2na . sub . 3 cit . 2h . sub . 2 o 2 . 04 8 . 7 4 . 87 61 . 7control 0 8 . 1 5 . 24 61 . 6kal ( so . sub . 4 ). sub . 2 . 12h . sub . 2 o 1 . 43 8 . 3 5 . 04 60 . 1______________________________________
the burn rate of tobacco is decreased without impairment of its quality of smoking by the application thereto of small amounts of certain salts , preferably hydrated magnesium chloride , which upon heating exhibit a plurality of endothermic reactions at successively increasing temperatures in the range from about 100 ° c . to about 500 ° c . in addition , the presence of small amounts of an alkaline material such as calcium hydroxide is desired to counteract marginal changes in the yields of some smoke components and to increase smoke ph .